Read the Budapest Memorandum on Security Assurances, from 1994. (Ukraine gave up their nuclear weapons.)

When Russia entered the Crimea in 2014, Obama and Biden gave the Ukraine military blankets, Trump gave the Ukraine military Javelins missiles that were a good defense against the Russian tanks. No surprise Putin went into Ukraine under Biden's watch, in order to take over Kyiv (or Kiev), the Capital of the Ukraine.. https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Security_Assurances