I know South Korea and North Korea are still in a state of war. Similarly for Israel and Lebanon. And it seems Russia and Japan are also, technically, in a state of war. The last, if true, is surprising (as it is not something you would think every day). I wonder if there are other armed conflicts between recognised countries that I am not aware of? (so Israel-Palestine is another example, depending on the legal view of Palestine as a country)
3There are some others to be found here, but this is not a clear-cut list: en.wikipedia.org/wiki/Frozen_conflict– EvargaloMay 3, 2018 at 15:59
5This question is complicated by the ambiguity of what constitutes a "state of war", especially since formal declarations of wars have fallen out of favour in contemporary times. @Evargalo This Wikipedia list springs to mind: List of longest wars. Sort by "End Date" to see ongoing ones. OP - if the list does not answer your question, please edit your post to clarify and explain why it doesn't. Preferably, we would like a question with a relatively specific answer.– SemaphoreMay 3, 2018 at 16:09
4No, Russia and Japan are absolutely still in a technical state of war. Russia inherited the diplomatic relations of the Soviet Union, and a state of war doesn't need reciprocal declarations of war to exist. Both Japan and Russia have referenced the Kuril Islands as an obstacle for a peace treaty after 1991.– SemaphoreMay 3, 2018 at 17:45
1If those are your premises (1) that one country inherits the diplomatic relations of it's predecessor and (2) it only takes one country to engage both in war unless peace is formally agreed too. Then the United States is at war Red China from the declaration of the Qing Dynasty of 1856 and Croatia from 1941. Oh and of Coarse Iran who declared war unilaterally on the US in 1989.– user20338May 3, 2018 at 19:24
3@JMS Except Qing China formally made peace in 1860 with the Treaty of Tientsin, and the current Republic of Croatia refused to recognise the WW2 Independent State of Croatia as its predecessor. In contrast, the Russian Federation explicitly declared itself the continuator state of the Soviet Union, and thus - with the approval of the international community - by law took over the former USSR's external relations, e.g. the UN Security Council seat. So, it is not my premise, but rather your ignorance of the succession of states.– SemaphoreMay 4, 2018 at 5:36
Correlates of War and Inter-State Wars
The best data set I know of for war-related research is the Correlates of War (CoW) project. CoW has been operating at the University of Michigan since the 1960s and has been used in many professional (academic) publications.
They categorize wars into four types based on who is fighting. You are describing inter-state wars (wars fought between different states). Their data was last updated in 2007. At that time, there were no on-going inter-state wars. The most recently completed war is the United States invasion of Iraq in 2003.
CoW publishes a guide describing how the count and categorize wars. One important caveat is that they don't count anything with less than 1,000 battle-related fatalities among all participants. So it's conceivable that small wars are slipping by.
This is not an entirely correct answer but sort of interesting. I have sometimes read that the Second Seminole War of 1835-1842 is technically still ongoing since there never was a peace treaty signed.
Note that technically the Seminole people are not a country, being considered to be a domestic dependent nation within the USA. I don't believe that the US Congress ever declared war on the Seminoles but merely appropriated funding for the war effort.
As the war wound down various Seminole groups agreed to leave Florida and be transported to The Indian Territory. There never was anything like a peace treaty with all the Seminoles. In 1842 Colonel Worth received permission to declare the war over, and did so on August 14, 1842.
The Third Seminole War ended the same way, with many Seminoles captured or surrendered and being shipped to The Indian Territory, and Colonel Loomis declaring the war over May 8, 1858.
The Second Seminole War can be considered legally similar to the American Civil War, with a group of US subjects and/or citizens revolting against the government. There was never any peace treaty with the CSA. Instead President Andrew Johnson proclaimed that that the insurrection was ended in all the south except Texas on April 2, 1866, and a total end to the war on August 20, 1866:
"And I do further proclaim that the said insurrection is at an end and that peace, order, tranquility, and civil authority now exists in and throughout the whole of the United States of America."
So if anyone claims that the Second Seminole War is still ongoing, a sort of "frozen war", would they also claim that the US Civil War was also a sort of "frozen war", or would they claim that they are different?
They could claim there is an important difference between a proclamation of the war's end by a local military official and by the President, for example. Or they could claim that the federal government of the Confederacy no longer exists and that Seminole tribal governments do still exist, making the Seminoles more capable of waging war than the Confederacy is.
So I suppose that there is room to question whether the Second Seminole War has officially ended in a peace or if the fighting has merely slowed down and stopped for over a century and a half?
You made me look up the seminole tribe of Florida. Their website says: "The Seminole Tribe of Florida is a Federally Recognized Indian Tribe, the only tribe in America who never signed a peace treaty."– John DeeMay 3, 2018 at 22:57
1Of course saying that they never signed a peace treaty is not the same thing as saying that they are still at war. I'm sure that the writer didn't intend no peace treaty to be interpreted as "still at war, and therefore the USA should attack us sometime to force us to surrender", but more like "interestingly, our tribe could possibly be considered to be still at war with the USA".– MAGoldingMay 3, 2018 at 23:04
2"Peace treaty" isn't the only way for a war to end. A war can also end through "debellation", where one of the combatants ceases to exist.– MarkMay 5, 2018 at 1:22