* It supplies most ammunition and arms and much of the equipment.
* It funds most of the war effort, including arms & ammunition, salaries, covering some of the civilian budget etc. Total expenditure by "Western" countries in the period 2014-2026 is 380 Billion USD [1] and the vast majority of that is by NATO; some by other US allies.
* Its members train Ukrainian forces.
* It imposes wide sanctions against Russia (along with a few other US allies).
* Ukraine has already signed off half of all of its material resources to the US, the lead state of NATO [2].
* A negotiations process in Istanbul, having reached a draft agreement which would have concluded the war, in early 2022, was vetoed by NATO, or at least the US and the UK. [3]
And this is in the context of NATO's long-standing strategy of expanding eastwards towards Russia, which includes introducing Ukraine into its sphere of influence and possibly inducting it as a member at some point.
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[1] - https://en.wikipedia.org/wiki/List_of_financial_aid_to_Ukrai...
[2] - https://en.wikipedia.org/wiki/Ukraine%E2%80%93United_States_...
[3] - https://responsiblestatecraft.org/2022/09/02/diplomacy-watch...