This is really a huge question and we cannot come close to answering it all in this space. I will mention two major impacts such changes have had on US society.
The major economic change after WWII was the fact that the US became the richest country in the world and the American standard of living shot up. This led to such things as the conformity of the 1950s and then the rebellion of the '60s. It led, you can argue, to our current attitude that says that the US should always be the richest country in the world and that our standard of living should grow rapidly forever.
A major change in population has been the growth in the numbers of racial minorities in the US. This has led to a much more multicultural US. It has also led to fears among some whites that "their" America is being taken away and that a new, less "American" America is being created. This is, one could argue, behind some of the "culture wars" that now exist in the US.