What do you think changed as a result of the war in regards to:
-Individual nation's policies
-Relations among the great powers
-Our former enemy countries
-Any long range obstacles?
The end of World War II signified the end of massed warfare -- never again will all the resources of one country or nation be pitted en masse against another -- once the Bomb existed, all-out warfare was a thing of history. WWII altered warfare. Since that time throughout the world, there has been armed conflict, but that was contained by the aforementioned superpowers. It's interesting to see now the rise of "indiscriminate" warfare, or terrorism, as the other forms of warfare expression have been neutralized.
One long range problem arising from the aftermath of World War II was the hostility of the Soviet Union toward the USA, which led to raising of the Berlin Wall and the overpowering of what became satellite states to form an East-West buffer to protect war ravaged Soviet territory.
One consequence of World War II seems to have been the rise of an increasingly integrated Europe, with France, the U. K., Germany, and Italy all playing major roles in the European Community. Part of the ideal purpose of the European Union seems to have been to make wars such as the two world wars less likely. Another part of the purpose seems to have been to allow Europe to function as a kind of superpower in competition with the U. S. and the former Soviet Union. Of course, the E. U. is having major problems these days, but it is hard to imagine another European war, in the near future, resembling the two world wars.
The role of the US worldwide was increased- remember that before the war elements on the left and the right supported nonengagement if not downright isolationism. As for relations between the great powers, the point is that many of the so-called "great powers" were not key players after the war, including Britain and Germany. I think it's important to recognize the scholarly debate on the subject of US influence in Europe vs. that of the Soviet Union. Recent scholars have observed that Stalin saw his actions as defensive rather than imperialistic, and that a reason for this was the proactive efforts on the part of the United States to establish Germany and other European nations as a western-style capitalist state. Another crucial topic that is not directly related to the categories laid out in the original post was decolonization, which helped to shape the course of the Cold War.
As a Brit, I think it is important to note the way that in the aftermath of WWII we lost some of our power and influence thanks to the rise in prominence of the USA and the USSR. We began a downward slide that has moved us away from being a superpower. Also something worth noting is the way that in the aftermath of WWII the concept of a united Europe was formed, which of course we now see in the European Union.
One of the unintended consequences of World War II was the build up of nuclear arms. It is actually ironic. The world saw what the power of an atom bomb could do, yet they built more nuclear bombs that ever before. The build up particularly in the United State and the former USSR was astronomical. The full impact is not yet known. For instance, we cannot account of all the missiles of the former USSR. That is a frightening thought.
Japan and Germany both became American allies after the war and they also became two of the wealthiest nations in the world, in part because they were not allowed to build up their military following the surrender. The aftermath of the war left only two world superpowers: the U. S. and the U. S. S. R. Great Britain remained a power, but not on the same level as the Americans and Russians.
Analyzing "individual nation's policies" in the aftermath of WWII has occupied many doctoral students and will continue to do so. In following the previous post, the changed relationship between the USSR and the USA, as summarized by the Cold War mentality, resulted in the escalation in the building of nuclear armaments and the creation of trade alliances between nations aligned on opposite sides of the Iron Curtain.
In terms of our former enemies, The Soviet Union wa spart of the Allied effort to defeat Japan and Germany, but once that had been achieved, they were enemies of the West in the Cold War. The wartime policy of an alliance of convenience quickly evaporated in the face of the opposing systems of government, and the USSR's desire to spread and foment revolution around the world while the US and allies sought to contain it.
I'm thinking that you're asking about WWII because your other discussion is about that time. The most obivous answer here is that our main two enemies became two of our closest allies after the war while the USSR beame our enemy.
But you could argue that that wasn't a result of the war but rather a result of communist ideologies and Stalin's actions after the war.
The major long range obstacle I see is that the US became convinced that it deserved to have a huge economic growth rate in perpetuity. We got spoiled by this time when we were so far ahead of the rest of the world that our economy grew very fast. Now, we expect that to keep happening because it's how things always were and we get angry when it does not.