Emperor Putin does not have a LW account, so he posted his answer in a book.
The sheer desire to dominate. Really it’s always a factor for any policy, the question is when it’s becoming seductive enough.
Putin, being mafia-style boss, needs certain balance of force inside Russia. Professional Armed Force means too much risk of military coup, while Soviet-style colossal conscript Armed Forces means too much risk of revolution in the case of mobilization, so Putin needs neither. His obvious solution is to have an Armed Forces with very sloppy trained soldiers and very inflexible, anti-intellectual, corrupt and fanfaron officer corps—so that they are constituting as little menace to him personally as it’s possible. To make such an army—you have to eliminate the most brave and responsible of these men in Armed Forces. To send them die in some ill-prepared war is a good solution.
A: Because Ukraine was shelling Donbas.
B: Because Ukraine was threatening to invade and conquer Crimea.
C: Because Ukraine was developing/threatening to develop weapons of mass destruction.
D: Because Russia is convinced that the west is out to get it, and the Russian people desire victory over the west, serving as a show of force and thus potential deterrent to future hostile actions.
E: Because Ukraine cut off Crimea’s water supply, and other such nettling actions.
Here we need the two dimensional voting, because these statements are all technically true. For example, considering point C, almost every country is producing or researching something that could be used as a weapon of mass destruction.
Zelensky clearly stated at the Munich Security Conference that if the west didn’t give him guarantees that he wasn’t going to get he would withdraw from the Budapest Memorandum. This is a declared intent to develop nuclear weapons, and is neither in doubt nor vague in meaning.
Russia also accuses Ukraine of developing bioweapons. All of the evidence for this comes through Russia, so I wouldn’t expect someone who didn’t already believe Russia’s narrative to believe said accusations, but in any case, bioweapons development is held by Russia to be among the primary justifications of the invasion.