This is a direct result of the Marshall plan in Europe, and the Macarthur equivalent in Japan, and was the direct creation of an anti-USSR alliance rather than allowing them to take over the entire continent. This was largely inspired by the observations the US had made over their post-civil war period.

Germany and Japan after WWII are absolutely NOT the norm for countries coming out of war. Throughout history they are pretty much the only examples, normally war through a place causes it to be utterly fucked for a long, long time. The main question of what happens with Ukraine is largely to do with the potential threat of Russia after the war. If Russia is a threat, then Ukraine will see a whole lot of investment as a direct NATO border with zero buffer states between. If it isn't, it will likely bleed brains to the west due to also joining the EU allowing free movement, and turn into a longterm backwater.