War is just politics, massive swing in politics (i.e. pull funding, without USA backing this would've never left the 2014 "Start") results in a massive swing in the war. The major goal of war is to change politics.
The US as the primary trainer and funder of one side has massive control. Multiple times the USA forces Ukraine to continue rather than work on peace deals over the past 4 years .
Crimea going from Ukraine to Russia "by vote" is the same exact model used by the eastern regions that started this 2021 excursion