How have the wars since WWI shaped the lives of working class people in the U.S.?
The various wars America has been involved in have had many effects. The earlier wars (WWI, WWII, and Vietnam in particular) have had a much greater effect than more recent wars such as those in the Middle East.
World War II had the greatest impact as it was the biggest war. It had the impact of completely remaking the lives of many working people after the war. The US entered a time of great prosperity after the war, making it much easier for working people to make a good living. In this sense, the war was a boon to those working people who were not killed or badly injured in it.
Later wars have tended to have a more negative impact on the working class. They have been fought by a military made up more and more of working class people. This started with the draft in Vietnam and has continued through today's military which is overwhelmingly made up of people from the working class. It is almost fair to say that today's wars are being fought by a very small segment of the working classes of society, thus putting the major burden of the wars on that class.