Seeing as how Afghanistan is being taken over by the Taliban and remembering how easy it was for ISIS to just roll over the Iraqi Army, plus the role of Al-Qaeda in starting these two wars, it got me wondering just what exactly are the differences among the three groups?
|Attack civilians in
|Military operations||Can be engaged
|allowed Al Qaeda operations
leading to 9/11
|✔✔✔||up to 2001: somewhat
2016-present: Trump, Biden
|ISIS||✔✔✔||✔✔✔||✔✔ (not very capable against hard opponents)||no|
ISIS and Al-Qaeda are transnational terrorist networks aiming to either set up a caliphate (ISIS) or punish the crusaders (Al-Qaeda).
Since 2001, the Taliban has used terrorist tactics (attacks on civilians), as well as standard insurgency tactics (attacks on military/governments targets) to re-establish an Islamic Republic in Afghanistan. From 1994 to 2001, the Taliban controlled Afghanistan and abused its population. They also allowed Bin Laden and Al Qaeda to operate from their territory.
ISIS and the Taliban have both persecuted and executed civilians on their controlled territory. Prior to 9/11/2001, while the Taliban controlled Afghanistan they were operating a quite harsh interpretation of Sharia law: many forms of entertainment were banned, women were strictly controlled and were limited in education, summary punishment, up to executions, was handed out. Minorities were sometimes massacred. Still, overall, the Taliban claimed to be driven by recognizable notions of Islamic justice as per Sharia law.
Compared to the Taliban, ISIS were far worse, engaging in practices as sex slavery, massacres, and fairly routine executions.
Al Qaeda never really went after territorial control, remaining mostly underground, so they didn't systematically persecute civilian populations in their base area.
Both Al Qaeda and ISIS carried out a number of attacks against Western civilians in Western countries. The Taliban mostly only attacked Westerners in Afghanistan (and maybe Pakistan? Daniel Pearl was an Al Qaeda, not Taliban, victim).
The Taliban has at times courted international recognition and diplomacy. There are also theories of fairly chummy relations with Pakistani intelligence. Neither Al Qaeda nor ISIS have engaged with any countries at that level (which does not preclude them having received support by sympathetic countries). Things are never simple: the "Pakistani Taliban" (which is related to, but not exactly the same) has occasionally engaged in terrorist activities against the Pakistanis.
In short, Taliban, minus their 2000-2001 tolerance for international terrorist groups like Al Qaeda on their territory (which culminated in 9/11), is something the West can probably live with, even if the Afghan population will suffer harshly if they revert to pre-2001 behavior. This is essentially what Trump, and then Biden, have gambled on in negotiations.
Neither Al Qaeda, nor ISIS, are groups Western countries can tolerate as their express goal is to attack Westerners abroad, outside their base area, they recognize no government control and are not interested in diplomacy.
It is quite possible the Taliban will avoid supporting international terrorists as it might trigger another set of actions against them. Whether or not they will return to their notorious pre 9/11 behavior towards the Afghan population is something time will tell. The signs are not necessarily good right now, but then again the people making claims of duress have every interest in drawing Western forces back in.
Let's start what those 3 groups have in common first. They all are militant groups trying to achieve their goals by military force and they all are trying to impose a hardcore version of Sunni Islamic law on some territory. Islamic law implies harsh punishments for large number of crimes and all those groups will attempt to prosecute people that they believe to be criminals. That includes treason by cooperation with enemy of Islam and blasphemy by following 'wrong' religious practices which typically means that whenever they capture some territory they have a lot of "criminals" to persecute. These laws are essentially medieval, so they look quite barbaric to us, but to be honest, there are countries like Saudi Arabia that have broadly similar laws.
Now let's look at the differences.
Taliban is a nationalistic Afghan movement. They are trying to establish Islamic law only in Afghanistan and expel foreign forces only from this territory. They don't mind coexisting with other nations so they are trying to establishing diplomatic relations, proceed with trading etc. and might be willing to even make some concessions to make this happen.
Islamic State have much more ambitious plans. Their views are based on idea that long time ago there was a country that united all Islamic people, a Caliphate. Then Western "crusaders" came and divided Caliphate into several group of artificial nations, putting them under foreign rule and setting against each other, inciting wars and unrest between different groups of Islamic people. Think division of Ottoman Empire as an illustration of this concept. ISIL goal is to "restore" this Caliphate, uniting all Islamic people in one country and it's willing to serve as a government of this new country. They view any resistance to their plans as betrayal of Islam and assistance to foreigners that divided the Caliphate.
Al Qaeda goals are broadly the same, but while IS aims to directly conquest "Islamic lands" and establish their own government, Al Qaeda instead tries to impose Islamic law on those lands by working with existing government. They think that it's simply not necessary to be part of a formal government to persecute guys that violate Islamic law. They also assume that every Islamic nation already have mostly "good" guys that will live according to Islamic law if they will be free from oppression of largely external "enemies". So they aim to 1) prevent foreign intervention and 2) kill or intimidate local "bad" guys that block "good" ones from coming into power. Once all local governments are free from interference and follows Islamic law they will happily unite into a Caliphate without need to fight wars between Islamic people.
As you can guess, with this mindset Al Qaeda is generally happy to cooperate with both Taliban or IS. They are sort of more idealistic and assume that local "criminals" are mostly "inspired" by foreign influence. However this also means that they are very aggressive towards western countries and are trying to use terror to force western world to "self-isolate" themselves from Islamic world.
Unlike other groups IS is very aggressive towards local (Islamic) population because they view all existing Islamic nations as foreign constructs and unlike Al Qaeda aim to destroy these rather than change them from within. This means that they target broader class of civilians. Just following Sharia law is not enough to be safe from IS because any sort of support to existing government is viewed by IS as assistance to foreign invaders. Therefore they are natural enemies of Taliban and they eventually became enemies with Al Qaeda because they thought that Al Qaeda betrays their ideas by cooperating with existing governments and Al Qaeda thought that IS is killing too much "good" Islamic people.
Taliban is sympathetic to Al Qaeda ideas and follows behavior "expected" from government by Al Qaeda, so they were allies in the past and could be allies in the future if they will. The key difference can be thought that Taliban is mostly interested by internal affairs of Afghanistan while Al Qaeda is concentrating on external affairs.