John Mearsheimer is wrong on Ukraine.
There are several popular videos by historian John Mearsheimer in which he argues that the war in Ukraine was caused by the West, based on his theory of "Great Power Politics". In his opinion, it was the West (mainly the USA) that provoked Russia with NATO's expansion. Mearsheimer argues that any Russian leader would have reacted like Putin did to NATO expansion, and any country in Russia's position would have acted the way Russia did.
From his point of view, Russia's invasion of Ukraine is a defensive war.
Mearsheimer points to Putin's own speeches and writings, in which Putin repeatedly opposed NATO expansion.
Here is why i think that Mearsheimer is wrong. His facts are right, but there are other facts that he neglects.
First of all, he reads the documents in which Putin talks about NATO and not the documents in which Putin reveals his Osama-like radicalization. Putin views himself in messianic terms, a prophet on a divine mission to restore the old imperial Russia and save the world from the perverted evil West. That's exactly how Osama bin Laden saw himself. Putin has written extensively about himself as the savior of Christian values.
See this article of mine.
Second, Russia is doomed to be expansionistic. Its entire history is a history of endless expansion, conquering countries and tribes that posed no danger to Russia but that... could have. Because Russia doesn't have natural borders, any neighbor of Russia constitutes an "existential threat" to Russia. Russia is doomed to view any neighbor as a potential threat, and therefore Russia views its many invasions of other people's lands as "defensive" wars.
Russia doesn't view itself as a colonial empire that has subjugated other people, but as a peaceful country surrounded by potentially dangerous neighbors, which are therefore to be eliminated.
If Russia bordered on Romania instead of Ukraine, it would consider Romania as an existential threat.
See "Russia the ever Expanding Empire" in this article of mine.
Third, Mearsheimer assumes that, when he gives speeches, Putin is talking to us. I think that Putin mostly talks to Russians.
His tirades against NATO are meant to stir up anti-NATO sentiment within Russia, which in turn justifies the "special operation" in Ukraine. I tend to read almost everything that Putin says as meant for domestic consumption.
The thing that freaked out Putin was the prospect that Ukraine would become a functioning democracy. It is humiliating enough that Poles and Czechs and Lithuanians live in freer and wealthier countries than the Russians who used to occupy them. It would be enormously humiliating if even Ukraine (the birthplace of the Russian civilization) became a prosperous democracy. Russians are willing to live under Putin's regime as long as they perceive economic benefits. Most Russians don't know that China's GPD per capita just passed Russia's: the Chinese are richer than the Russians. Most Russians identify only marginally with the Baltic republics (whose GDP per capita is double Russia's). But they do identify with Ukraine and Belarus, and it would be almost impossible to hide it from the Russian public if Ukrainians became richer and freer.
Mearsheimer thinks that Putin has a point when he demands
a buffer zone between Russia and the "West". Somehow, he doesn't realize that the "West" (which at this point is really eastern Europe) does not demand such a buffer. Somehow it is only Russia (the colossal nuclear power) that is fearful of bordering on European countries (Poland, Romania and so on). Why is Russia so afraid of bordering directly with eastern European countries that have become part of NATO and the European Union? Because Putin doesn't want Russians to know how much better the people of eastern Europe are doing.
The real "red line" for Putin was not NATO expansion but the very democratic election of Volodymyr Zelensky in 2019 (and before that the Euromaidan protests of 2013-14).
I bet if NATO told Putin: "Ukraine will become a member of NATO but it will always be run by a dictator", Putin would not object. It's not NATO membership that scares Putin, it's a democratic Ukraine that scares Putin.
This does not mean that Putin's anti-NATO rhetoric is just for show. Putin truly fears NATO, but not because he fears that NATO will invade Russia (an incredibly silly idea: imagine Spain or Italy or Hungary agreeing to invade Russia - it takes the consensus of all members) but because he fears that NATO will treat him like NATO treated Qaddafi.
Putin is known to have watched the video of Qaddafi's execution over and over again.
NATO never invaded Libya and didn't even start the protests against Qaddafi, but, after the riots started, NATO helped the Libyan people kill Qaddafi like a dog.
However legitimate this fear, it makes no difference if the border with NATO is in Romania or Ukraine, so invading Ukraine was not going to change this.
Indirectly, Mearsheimer assumes that Putin is an idiot. If NATO expansion was Putin's main concern, he should have foreseen the consequences of invading Ukraine, notably that Finland would join NATO. According to Mearsheimer's own theory, now NATO poses an even bigger existential threat to Russia, bigger than it was before the war. I instead think that Putin doesn't care what Finland does. Putin knows that neither Finland, nor Germany, nor Italy, nor Spain are contemplating an invasion of Russia. NATO is no existential threat to Russia, and not even to his regime. After all, NATO let Putin slaughter half a million people in Chechnya, even welcomed his intervention in Syria, and tacitly accepted his annexation of Crimea.
The existential threat to his regime would be a prosperous democratic Ukraine.
That would screw up his divinely-ordained mission to recreate the "third Rome".
And he does profoundly despise the Western countries, which he views as decadent and evil.
Not because they pose an existential threat to Russia but because they pose an existential threat to his moral values.