The only reason Russia is invading Ukraine is because they feel threatened by the USA and NATO and they need a buffer for their own defense. If USA left NATO and especially if Russia joined after that then Russia would not feel the need to secure a buffer between NATO and Russia.
China probably would not feel as threatened either if the USA were not as involved in Asia as it is currently. I think the world could actually reach a new level of peace if President Trump would withdraw the USA from NATO and isolate the USA from world politics.
It isn't isolation, it is non-intervention, and not getting into entangling alliances.
There can be no greater error than to expect, or calculate upon real favours from Nation to Nation. 'Tis an illusion which experience must cure, which a just pride ought to discard. ~ George Washington
My policy has been, and will continue to be, while I have the honor to remain in the administration of the government, to be upon friendly terms with, but independent of, all the nations of the earth. To share in the broils of none. To fulfil our own engagements. To supply the wants, and be carriers for them all: Being thoroughly convinced that it is our policy and interest to do so. ~ George Washington
The great rule of conduct for us, in regard to foreign nations, is in extending our commercial relations to have as little political connection as possible... Why, by interweaving our destiny with that of any part of Europe, entangle our peace and prosperity in the toils of European ambition, rivalships, interest, humor, or caprice?... It is our true policy to steer clear of permanent alliances with any portion of the foreign world. ~ George Washington
The true theory of our Constitution is surely the wisest and best, that the States are independent as to everything within themselves, and united as to everything respecting foreign affairs. Let the General Government be reduced to foreign concerns only, and let our affairs be disentangled from those of all other nations, except as to commerce, which the merchants will manage the better, the more they are left free to manage for themselves, and our General Government may be reduced to a very simple organization, and a very inexpensive one; a few plain duties to be performed by a few servants. ~ Thomas Jefferson
[America] goes not abroad, in search of monsters to destroy. She is the well-wisher to the freedom and independence of all. She is the champion and vindicator only of her own. She will commend the general cause by the countenance of her voice, and the benignant sympathy of her example. She well knows that by once enlisting under other banners than her own, were they even the banners of foreign independence, she would involve herself beyond the power of extrication, in all the wars of interest and intrigue, of individual avarice, envy, and ambition, which assume the colors and usurp the standard of freedom. ~ John Quincy Adams
Can any reasonable man be well disposed toward a government which makes war and carnage the only means of supporting itself? ~ Alexander Hamilton