just big enough said: you maybe over estimating the US role in modern day, part of this conflict is Russia not wanting the US on its boarders, Ukraine were doing very well with the help received from Europe, Russian tanks and aircraft are not being destroyed by American weapons, and very difficult to move howitzer are being destroyed by more agile Russian mortars. If the US leave Europe a war in 25 years is unlikely, the biggest threat in Europe is Russia distain for America and putin is Constantly reminding the world of that putin made it very clear when he put his troops on Ukraine boarders he did not want them as part of NATO for reasons above so you could argue US involvement in Europe was a keystone in this conflict starting. NATO is a group of countries working together as equal members and that is how NATO will stay nobody views US as the key player in this that's Trumps view.
Disagree. US pulls out, Europe -- and Germany especially -- will rearm. With a population of around 600 million (almost twice the population of the US and almost three times that of Russia), the EU could field a military larger than the US or Russia, as they have the population and the resources. If and when that happens, Russia would respond in kind. Russia fears a rearmed Germany more than they fear the US, as they have fought two devastating wars with them just within the last 110 years.
It is not well publicized, but Russian military leaders still view Germany as a potential threat to Russia. They were very hesitant to let Germany reunite because of it. The view of Germany as a potential adversary is something reinforced every Victory Day on May 9 in Russia -- The Great Patriotic War wasn't fought against the US, after all.
If the US pulls out of Europe, and Germany re-arms to fill the void (which it would, because they particularly would feel vulnerable against Russian threats), there will probably be war on your continent within 25-30 years, probably between Russia and the EU. Europe is a continent with a long, long history of war, that only ended (for the most part -- if you exclude the civil war in Bosnia and Yugoslavia) in 1945, and there is no guarantee that it would or will never happen again.
Why do you think the EU was concerned about the UK pulling out of the EU? It's for the same reason they didn't like the idea of Trump pulling the US out of NATO. They realize that the US, as well as the UK, were moderating influences on the continent, both in the EU's dealings with Russia militarily, but also moderating influences on rivalries within the EU, and they also knew that the military presence of the US and UK in NATO would help prevent a greater European war.
US involvement was not a keystone in the Ukraine War starting. NATO leadership allowing NATO to be expanded east to the Russian border was a keystone in the Ukraine War starting. There's a difference. The US was not the only member pushing for expansion eastward. I have yet to read of any EU leader saying "NATO shouldn't expand east", although there may have been some saying that, that I haven't read about. The EU contingent in NATO went along with it. They didn't try to stop it. in fact, the EU itself expanded east to Russia's borders, and the EU has its own international military (called PESCO), which could be expanded into an EU military should the EU further integrate their governmental and military operations. How do you think that idea is viewed in Moscow?
Either way, from the ground in Ukraine, this discussion is beside the point. Innocent people are getting slaughtered, and to them it's not a problem of how the war started, but how to end it to stop the killing. The best thing is to end the war, with Ukraine being intact, and working out a new provision for peace in eastern Europe.