No, it didn't.
If they USA did nothing, russia would still not be the slightest threat to the usa
How exactly does "a war happened halfway around the world" prove isolationism does not work?
You see, this here is exactly where isolationist thinking goes wrong, because it only thinks in the 'right now.'
Does Russia taking control of Ukraine threaten the US?
Only a little bit, and that's economically. It's a much bigger threat to Europe, but again, that's not a direct threat to the US.
What about when Poland is next?
No, it's only a modest economic threat, no major threat overall. Poland is even less important to the US economy.
Moldova? Romania? Latvia? Estonia? Lithuania?
None of those are that big a deal to America either, economically or militarily, but at this point, Russia has just about finished reconsolidating the Soviet Union.
And then Germany is next.
And at that point, it
is a big damned deal, because if
Germany falls, then either Russia will get all of Europe, or we're going to have WWIII. And we really,
really do not want either of these outcome. More, the price of stopping Russia is a lot steeper now, because now the Russians have the (depreciated but still present) economic and military power of all the nations they've absorbed behind them, even if they get shit on like the people in Donetsk and Luhansk are right now.
No, instead it is much,
much better to just give money, munitions, and material to the Ukrainians to stop all of this now.
To use the tired old WWII analogy, imagine if instead of declaring war when Poland was invaded, and doing shit-all to actually stop the Germans, the allied powers had denied Germany the sudetenland, and because they didn't want to actually
fight another war due to scars from WWI, had just funded the Czech war effort when Germany tried to invade to take it anyways.
TL;DR: It isn't just about Ukraine, it's about the precedent it sets, and whether or not the great powers of the world will let things devolve into another round of Cold War.