Broadly speaking, it’s because Putin is pissed that the Soviet Union fell (he lived through it as a KGB member in East Berlin), and Russia culturally originated around Kiev (https://en.wikipedia.org/wiki/Kievan_Rus%27), so he sees it as part of what should be the Russian empire. There are some important industries and resources in Ukraine, plus better access to the Black Sea. Ukraine’s orientation towards the EU and NATO is seen as an ideological and military threat. But the perceived humiliation of the fall of the Soviet Union, not being respected in the Western world, and trying to undo that and restore Russia’s glory, seems to be what is driving Putin the most.

It surprises and scares me how few people in the West understand this. It's because staring wars is how dictators cling to power, plain and simple. This is obvious to anyone who follows Russian politics. There's even a term "Crimea consensus", referring to the fact that annexing Crimea made Putin super-popular again after he angered people with his clumsy return to the presidental chair. In 2022 his rating was at all-time low again.

Yes, it's actually a bit more complex than that. Russia never stopped being an empire, it's codifed in their culture in many ways. Yes, there are personal inclinations of Putin. He said in his first ever interview when he got some minor post on SPB government that the Bolsheviks' greatest mistake was giving autonomy (however nominal) to the soviet republics. So those are the reasons too. What's not a reason in any way though is geopolitics. Feeling threatened by NATO, needing this or that resource, access to this or that body of water, fighting Western colonialism (!) - those are all bullshit reasons invented for propaganda.

We're 3 years in and I have zero idea. Nothing comes to mind except for plain old expansion for the sake of expansion.

Historical: Putin longs to rebuild Russian empire

Strategic: oil, minerals, Black Sea port access. Russia's great strategic weakness is that it doesn't have any warm water ports, which drastically limits its naval reach and ability to shape trade.

to rebuild USSR aka russian empire. That includes EU "eastern block" countries.

This is an absurd claim

Are you serious?

It's complicated because you hear so many different stories and versions as to why. My take is they regard Ukraine as basically Russian land and put up with Ukraine being independent when they had a pro Russian government but got annoyed when the Ukrainians, with American help, overthrew that and went western democracy.

But it's also part of a long pattern - over the last 500 years Russia has expanded at an average rate of 50 square miles per day by invading other people's countries and the like - it what they've always done. I'm not sure if that isn't a bit out of date these days - the whole imperial invasion thing. I mean I'm a Brit and we used to do it and had the world's largest empire but it's all a bit passe now. (50sq mile link https://www.foreignaffairs.com/articles/ukraine/2016-04-18/r...)

By the way re the history, Ukraine, governed from Kyiv is basically the same as Kievan Rus, also similar land governed from Kyiv and existed long before Moscow or Russia were invented. Muscovy, the bunch out of Moscow, were a warlike lot and stole the Rus bit of the name and much of the land. So when you here Putin going on about it not being a real country and just a bit of spare land belonging to Russia, it's not quite true.