I have been hearing on the news that Gaza is under attack. I understand that this is a hot topic. I want to know why Gaza is being attacked now (May 2021), who is attacking, and what they want.
Since you emphasize the word now in your question, I'll try to answer with an emphasis on the current escalation. For the more general question asking why there is a conflict at all, I'll simply refer to the Wikipedia article because it's such a complex issue that I cannot explain well.
So the questions I'll try to address are as follows:
I want to know why Gaza is being attacked now, who is attacking, and what they want.
Which parties are fighting?
The parties in conflict are the state of Israel and Hamas. The state of Israel has an advanced military, the IDF, that it uses to defend itself. Hamas is classified as a terrorist organisation by a number of countries (including the US, the EU and Israel), but it also controls the Gaza Strip.
What are the parties fighting for?
Hamas' aims are, according to Wikipedia:
Hamas, as its name (Islamic Resistance Movement) implies, aims to liberate Palestine from the Israeli occupation, and transform the country into an Islamic state. Which of these two objectives is the primary goal is disputed.
Israel is a state and its current military operations in the conflict are described as self defense. For example, in an interview with Face the Nation, Israeli PM Netanyahu said:
And I think any country has to defend itself. It has a natural right of self-defense. We'll do whatever it takes to restore order and quiet and the security of our people and deterrence. We're trying to degrade Hamas's terrorist abilities and to degrade their will to do this again.
I am not aware of any concrete demands that motivate the fighting in this current episode of violence.
This is the more interesting emphasis of your question. The previous answers are more general and could apply to previous escalations alike. One of the reasons the fighting has escalated as far as it has or has gone on for this long (Wikipedia's timeline for the current escalation starts on May 6th, though it considers heightened tensions in the weeks leading up to that) is political.
Specifically, on both sides of the conflict there are people in power who can use the escalation as a distraction from their own internal politics. As such, I'd argue that it's not just the events in the timeline that explain the lead up to the current level of violence. On both sides, the leadership has taken steps that are escalatory in nature, not aimed de-escalating the situation.
Continued war rhetoric from Israeli PM Netanyahu
Note that he isn't phrasing the military response as self-defense, instead he uses language of revenge ("levy a heavy price") and strength ("full force"). According to the Hindustan Times:
In a televised address, Netanyahu said Sunday evening the attacks were continuing at “full-force” and will “take time.“ Israel “wants to levy a heavy price” from Gaza’s militant Hamas rulers, he said, flanked by his defense minister and political rival, Defense Minister Benny Gantz, in a show of unity.
That rhetoric may seem insignificant but it's adding more oil to the fire. That directly benefits Hamas because it needs the perception of Israeli aggression to justify its actions and to remain popular with Palestinians.
Hamas setting an ultimatum that promises violence if not met
That's not a diplomatic request. Basically, it's setting up a justification for escalating further. According to nationalpost.com:
In Gaza, a Hamas spokesman said the leadership of a joint command of armed movements in the Palestinian enclave had given Israel “an ultimatum until 6 p.m. (1500 GMT)” to withdraw its security forces from the al Aqsa mosque compound and Jerusalem’s Sheikh Jarrah neighborhood.
Escalating won't resolve the conflict
We see that there's some escalating on both sides, but couldn't that serve some genuine purpose (as seen from their own perspective in the broader conflict)? If indeed it is in the best interest of the state of Israel or the Palestinian people (rather than just their respective leaderships) then it makes sense to escalate. I think the answer is no, there's nothing to be gained by escalating further.
The Israelis will not defeat all of Hamas, so escalating means there will be more violence in the future. Hamas will use any Israeli attacks to gain popularity and boost its recruitment. As anecdotally illustrated by one young recruit who was quoted by Haaretz:
Hatem, one of the teens who attended Hamas camp, is just 14, but he has already lived through three wars with Israel. Now, he’s proud of being ready for the next war. “The Israelis killed my niece last summer. Now I want to kill them,” he told the AFP news agency after finishing the camp.
From the view of the Palestinian people, it doesn't make rational sense to escalate either. Their weapons are much less advanced, so any attack will be returned multifold. This is clear from comparing Israeli vs Palestinian casualties (both in terms of deaths and wounded), for example here.
In the end, the current episode of violence is not a conflict that can be won (by either side). The best explanation, I think, is that it's politically convenient to escalate now for both sides. The political considerations on both sides are as follows:
On the one hand, there is the fragile domestic position of Israeli PM Netanyahu. According to the Washington Post on May 12th:
For Netanyahu, the escalation of fighting brought a last-minute reprieve from what could have been the end of his record run at the top of Israeli politics. Earlier this week, a group of rival political parties were reportedly within days — even hours — of forming Israel’s first government not to include Netanyahu in 12 years.
Just before tensions exploded Monday, a disparate collection of Israeli right-wing, centrist and left-wing parties, united only in their goal of ousting Netanyahu, indicated they were nearly ready to announce they had the support of a majority of parliament members, clearing the way to form a governing coalition.
By the end of the day, the political process had come to a halt. For now, amid the unrest, the prospect of a non-Netanyahu government is frozen and, political observers said, may be out of reach entirely.
“They were just about to call the president and say we have reached a deal, we have a coalition,” said Gayil Talshir, professor of political science at Hebrew University. “The riot came just in time to prevent the change of government in Israel.”
The same conclusions were reached in Israeli media. According to a compilation in the Guardian, dated May 13th:
Lapid [Yair Lapid, the Israeli opposition leader] said there had been a “complete loss of control” and accused Netanyahu of “leading us to anarchy”. He added: “Jewish and Arab rioters have declared war on Israel, and there’s no response, no government, no police, no leadership.”
Writing in Yedioth Ahronoth, Israel’s biggest-circulation newspaper, the commentator Nadav Eyal said: “We are seeing dissolution; we are seeing the fracturing of our social compact.”
Louis Fishman, an associate professor at Brooklyn College, wrote in Haaretz that Netanyahu’s “greatest magic trick” had been to blind Israeli Jews to their state’s oppression of the Palestinians. “But even the most carefully constructed house of cards eventually starts tumbling down, and that exactly is what is happening now … Impregnable Netanyahuism, the work of a master illusionist, is shattering.”
Lapid said the events of the past week were “no excuse” for keeping Netanyahu in place. “Quite the opposite. They are exactly the reason why he should be replaced as soon as possible.”
On the other hand, Hamas faces a similar situation in its internal politics. According to a Washington Post column dated May 13th:
For Hamas, its entry into the fray comes amid a tangled intra-Palestinian squabble. It’s at odds with Palestinian Authority President Mahmoud Abbas, whose Fatah faction holds nominal sway over the West Bank. (In an earlier era, Israel allowed the emergence of Islamist outfits like Hamas in a tacit bid to undermine the strength of more-secular Palestinian resistance groups like Fatah.) Abbas decided to scrap long-anticipated Palestinian elections this month, further delaying any prospect of reconciliation among the bitterly divided Palestinian leadership and intensifying public frustration with the increasingly unpopular PA.
To illustrate how Hamas can benefit from the current violence, the following paragraphs of the same WP column further illustrate how Hamas benefits politically:
One Ramallah-based pollster and former Palestinian Authority official said: “From preliminary indicators, many people in the West Bank are admiring what Hamas is doing. We don’t know their motivations, but it was effective of Hamas to confront Israel on the basis of their support for the Palestinian people of Jerusalem.”
“Hamas does not actually want something from Israel,” wrote Michael Koplow of the Israel Policy Forum. “It is seizing upon the current moment as an excuse to capitalize on a unique opportunity within Palestinian politics, and the rockets that Israelis are sheltering from are Hamas’s effort to get a leg up on Fatah.”
Seems this latest cycle between militant rocket launches from Gaza to Israel and Israeli retaliations on Gaza started on April 23 and has been on-off ever since.
Palestinian militants in the Gaza Strip fired dozens of rockets into Israel on Saturday drawing retaliatory air strikes, the Israeli military said, after nightly Ramadan clashes between Palestinians and Israeli police resumed in Jerusalem.
The pre-dawn exchange of fire broke months of relative quiet on the Israel-Gaza frontier.
Rocket salvos fired after Hamas calls for attacks on Israel over Jerusalem unrest
Now, this apparently evolved into another set of violence, which is the larger ones we are seeing:
On 6 May 2021, Palestinians began protesting in Jerusalem over a forthcoming decision of the Israeli Supreme Court regarding the eviction of four Palestinian families from Sheikh Jarrah, a neighbourhood of East Jerusalem; under international law, the area in question, effectively annexed by Israel, remains a part of the Palestinian territories that Israel currently holds under belligerent occupation. The protests quickly escalated into violent confrontations between Jewish and Palestinian protesters. The following day, Israeli police stormed the compound of the al-Aqsa Mosque, a major Islamic holy site.
The violence coincided with Laylat al-Qadr, an Islamic day of significance, and Jerusalem Day, an Israeli national holiday. The confrontations occurred ahead of a planned Jerusalem Day march by far-right Jewish nationalists that was later cancelled. More than 300 people were injured, mostly Palestinians, drawing international condemnation. The Supreme Court ruling was then delayed for 30 days as the Attorney General of Israel, Avichai Mandelblit, sought to reduce tensions.1
On 10 May, two Palestinian militant groups, Hamas and Palestinian Islamic Jihad, began firing rockets into Israel from the Gaza Strip, hitting multiple residences and a school. Israel launched airstrikes against Gaza, including airstrikes targeting multiple apartment buildings.
Since the rocket launches and airstrikes began, at least 122 Palestinians have been killed, including 31 children, while seven Israelis have been killed, including one child. On 11 May, the Israel Defense Forces claimed that at least 15 of the Palestinian casualties were confirmed members of Hamas, and also claimed that some Palestinian civilian casualties were caused by errant rocket launches within the Gaza Strip. As of 12 May 2021, both Israel and the Palestinian National Authority reported injuries for at least 300 Palestinians and 200 Israelis.
The Guardian pinpoints Hamas' motivations more precisely to the Al-Aqsa Mosque's occupation:
The militant group Hamas has fired rockets into Israel from Gaza just minutes after the passing of its ultimatum for Israel to withdraw its security forces from the Jerusalem compound which is home to the al-Aqsa mosque, and from the Sheikh Jarrah neighbourhood in the city’s east.
But this was entirely Hamas' leadership decision to pull the trigger and this can either really driven by this particular Israeli action or they took it as a pretext is open to speculation.
Again however, why exactly now is unclear. Israeli settlement activity, against international law, is fairly frequent so why did this particular event boil over? There is going to group dynamics at the protest, local police decisions on how to suppress that protest and then a decision by Hamas to make it a reason to start launching its missiles. Without much goodwill on either side, much frustration and with apparently no great communication between Israel's leadership and Gaza's, it's fairly easy to see something escalate way out of proportion to its original cause.
For reference, here's Wikipedia list of past rocket attacks. You'll see various causes for them.
Why is Gaza under attack now (May 2021)?
Israel is attacking Hamas targets in Gaza because Hamas fired rockets at Israel on 10th of May 2021.
Hamas fired rockets at Israel on 10th of May 2021 because Israel refused an ultimatum by Hamas to remove police forces from the Al Aqsa compound.
Israel refused an ultimatum by Hamas to remove police forces from the Al Aqsa compound because protesters on the compound were throwing rocks at the Western Wall below.
Protesters on the compound were throwing rocks at the Western Wall below because an Israeli court began the eviction process of a Palestinian family from land owned by Jews prior to the 1948 war for Israeli independence.
A list of Hamas rocket attacks against Israel in 2021 can be found here. Partial lists of Hamas rocket attacks against Israel for other years can be found here. Many of them state the reasons for the rocket attacks when the reasons are known. It is not clear why Israel has not attacked Hamas positions for previous rocket attacks.
Most answers here lay down the timeline of events, but don't really answer the crux of the question: why now?
Indeed, the situation "on the ground" is not entirely new. Evictions, protests, political uncertainty, hung government - that all was happening with some regularity for a long time before. What's new?
First, we should acknowledge that there doesn't have to be something new; for this, I'll send you to the @Lawnmower Man's answer, which certainly deserves better attention. Most "trigger events" in history are just pretexts, while the situation might be ripe for years.
Yet, I'll try my own take.
What's new is the US government. Undisputably, this government is less Israel-friendly than the previous one. That opens some possibilities.
Hamas, being a terrorist organisation, doesn't seek military victory: they know perfectly well this is impossible. Even the terror they instill is not their direct goal: for Israel, this is a "kind of normal" and certainly expected background it is prepared for. The the more rockets they fire, the harder pushback they'll get, and again, they know it.
The main goal for Hamas is world's media attention. During Trump's time with his unconditional support for Israel, Hamas kept a relatively low profile and knew better than to launch massive rocket attacks. But now Hamas feels there is an opportunity to put itself back on the political map.
The rest is not new: in this media war, the harder the response is and the more victims on their own side, the more sympathy they can expect, and that's what they are trying to maximise. Given the precarious political situation in Israel, they feel the chances for hard-line retaliation are high, and that's good for them.
It will be nearly impossible to find a news source that is not biased one way or the other. Here is a Timeline from France24 (from 2021-05-11)
It begins the sequence of events with clashes at the Al-Asqa mosque in East Jerusalem, and cites discontent over evictions on settled land (that is to say, what was thought to be Palestinian territory under agreements of the previous generation), with the familiar cycle of drastic escalation and even more drastic retaliation. However, the narrative in this link is very thin on details.
The take-away here would be, in my opinion, that the cause precedes the firing of the first rockets.
From the Reuters link (2021-04-23) provided in another answer above:
Clashes and incidents of violence have occurred almost nightly in Jerusalem - a city holy to Muslims, Christians and Jews - since the start of Ramadan on April 13.
Palestinians say police have tried to prevent them from holding their usual Ramadan evening gatherings outside the Old City's Damascus Gate by erecting metal barriers in its amphitheatre-style plaza.
Israelis have been angered by videos on social media showing Palestinian youth striking or otherwise assaulting religious Jews in the city.
In response to an important comment by gerrit:
You could clarify that the Israeli authorities are evicting Palestinian tenants from disputed land. That means: from a Palestinian perspective, a foreign occupation force is forcibly removing Palestinians from their homes to make place for Israelis. From an Israeli perspective, the police is removing tenants from their home in accordance to Israeli law on Israeli territory.
@gerrit, that may be in the proximate case. More broadly here is a BBC article and in particular the BBC presents a map showing settlements, so one may draw their own conclusions about the dispute, in comparison to notions of Palestinian statehood, which were already limited by the Oslo agreements [area A/B/C maps, wiki]. Generally speaking, those limitations were not followed * [B'Tselem 2017] in regards to either the pattern of settlements nor handover of military and administrative[**] control of the west bank, according to the Israeli Information Center for Human Rights in the Occupied Territories, B'Tselem.
I don't claim to understand the byzantine details of the boundaries, so I will leave it at that.
[*] Take a look at the link with the asterisk above for more specific background on how events turned out in regards to the territorial divisions that were to be made per Oslo agreement (itself an unfinished process). This appears to be one of the irreconcilable differences in the conflict. The main political actors at the top, on both sides, have been in power for many years, so this background is pretty constant.
[**] In particular, had the handover of the administrative control of Area C taken place (as specifically intended by the 1995 agreement), then, if I understand correctly, then Palestinian side would have had authority for zoning, and the pattern of settlements, and exclusion areas around them, the lack of permitting, the evictions, and the conflicts resulting from all of the above, would have evolved in a drastically different way.
Mostly because Israel's current prime minister, Benjamin Netanyahu, is fighting for his political life. He's been under investigation for corruption since 2016, was indicted on relevant charges in 2019, and formally charged in 2020; his trial is underway as of the time of writing (May 2021). Should Netanyahu be found guilty, his political career - which has spanned over 30 years and five prime minister positions - would be over.
Netanyahu, the leader of the right-wing Likud party, has been fighting to have the allegations and later the charges against him dismissed since 2016, which is coincidentally the year that Donald Trump became President of the USA. While the previous President, Barack Obama, was a Democrat and therefore not wholly supportive of Israel's policies towards the Arab world, Trump as a Republican was almost the best ally that Netanyahu could ask for. With Trump's backing, Netanyahu was emboldened to vastly expand settlement activity (see e.g. Trump's order recognizing the Golan Heights as part of Israel), which naturally improved his profile amongst Likud voters while distracting from the allegations against him.
In 2020, with the possibility of Trump being replaced by a Democratic President less sympathetic to Israel's expansionistic policies, a prominent Iranian nuclear scientist Mohsen Fakhrizadeh-Mahabadi was assassinated, almost certainly by Israel. Again, this act deflected focus from Netanyahu's corruption case while increasing tensions in the Middle East; had Iran retaliated, there is a good chance that open war would have ensued between Israel and Iran, which would have guaranteed Netanyahu's position for its duration.
On 6 May 2021, Palestinians began protesting against an expected court order that would evict Palestinians from Sheikh Jarrah in East Jerusalem (an area of land captured by Israel from Jordan during the 1967 Six-Day War, and that had no Jewish families since 2000). This escalated into Palestinian protesters throwing stones from the grounds of the Al-Aqsa mosque (the third-holiest site in Islam, currently also under Israeli control). Israel responded by sending riot police into Al-Aqsa, firing tear gas, rubber bullets and stun grenades.
This inflammation of tensions was increased after Hamas issued an ultimatum to Israel on May 10, requiring the withdrawal of all Israeli security forces from the Temple Mount (where Al-Aqsa is located) and Sheikh Jarrah by 22:00 of that day. If this was not done, Hamas threatened that it and the other paramilitary groups in the Gaza Strip would resume attacks against Israel.
Since it's very unlikely that Israel would comply with this demand, the rationale for making it initially appears unclear. However, Mahmoud Abbas, the governing leader of Gaza/Palestine since 2009, recently indefinitely postponed long-overdue elections that were widely expected to weaken his Fatah party while strengthening their rivals Hamas; this effectively shuts Hamas out of political power, and presumably as a result they chose to remind all parties in the Israel-Palestine conflict of their power by making a demand of Israel that would naturally be rejected, thus giving Hamas justification for attacking.
As Israel did indeed ignore Hamas's directive, the latter resumed rocket attacks against the former, which has responded harshly with air strikes on the Gaza Strip, including on the headquarters of news organizations. This hardline response is consistent with Netanyahu's continuing attempts to deflect attention from his trial.
It's because both Israeli and Palestinian leaders are playing politics. On Israel's side, Netanyahu is using any and every thing at his disposal - including but not limited to military force - to deflect attention from his trial. In Palestine, Abbas's postponement of an election that would potentially see him unseated from power - which would lead to scrutiny of his personal finances, which he has been rumoured to be increasing using funds intended for Palestinian residents - has prompted Hamas to assert itself.
At the end of the day, peace suffers and ordinary people die because politicians would rather hold on to power than serve the people who have empowered them.
This concept comes from complexity theory, and you can read all about it on Wikipedia. Many systems in nature exhibit a power law frequency distribution, meaning that the frequency of an event is inversely proportional to (an exponent of) its scale. That is, an event that is 2x as large only happens 1/2 as often (multiply in whatever constant factor of proportionality is appropriate). But each event is ultimately the consequence of many, many smaller events in some sequence. Because of the highly nonlinear nature of the sequence, it is typically not possible to predict when the next major event will occur.
The canonical example is a growing sandpile. When you pour a steady stream of grains onto a sand pile, they will tend to accumulate near the top, while some grains roll down the side. Occasionally, a small stream of grains will tumble, and rarely, the pile will experience an avalanche and reorganize into a shallower configuration.
I would argue that many political events follow this power-law pattern because most political systems are a collection of thousands to millions of individual actors with varying degrees of political influence all jostling together for influence and control, with no straightforwardly predictable outcome at any scale. Most explanations of events are ad hoc ex post facto "just so" stories. We know this because precious few events are predicted in any detail before they happen. The few times that someone does manage to predict an event, it is often the case that they have also predicted many other events which didn't happen, leading to low overall accuracy.
This is not to say that politics is entirely unpredictable. Of course, certain geopolitical actions will lead to a variety of relatively predictable responses. But surprising turns of events should not really surprise us, because often these are the culmination of many grains of sand building up pressure at the top of the pile before they cause an avalanche.
Most importantly, political actors at the highest level are constantly trying to judge and predict the outcome of the most likely actions by themselves and others within their sphere of influence. This constant mixing of feedback produces more than enough non-linearity to make the results highly unpredictable. Usually when there is political stability, it is because competing interests have achieved a kind of temporary stalemate, where not much can be gained by any side until there is more external disturbance to the system. However, any kind of disturbance, by any actor, can set off a chain of events which cause an avalanche in an apparently unrelated but actually connected area.
Thus, we can talk about proximate causes with some accuracy, but larger-scale ultimate causes are probably too subtle and buried under too many layers of events for us to describe them conclusively. This is why historians are constantly reinterpreting history. It's not that the previous generations of historians were idiots, but rather there are always new perspectives that can describe what appears to be a separate chain of causes which, in fact, describe the same avalanche, merely from a different angle. To say that a final grain of sand caused an avalanche is to ignore the thousands of grains which made the scenario possible in the first place.