Then World War II has two more effects: it finally kicks the U.S. economy into gear through massive government spending but maybe more important the rest of the first world (Europe and Japan) has most of it's infrastructure heavily damaged. The only other potential competitor, the Soviet Union, disengages from the capitalist economies of the 1st world and builds it own 2nd world of communist countries. This leads to spectacular growth in 1950s and 1960s for the U.S. and with the New Deal consensus it mostly goes to the working class and the middle class.
In the 1970s, the consensus starts to break down primarily due to two factors: automation and globalization. The rest of the world begins to recover and compete. And because thy haven't had the same sort of growth the U.S. did, their workers are much cheaper. Additional automation begins to create an ever-lowering ceiling on how much a low skill job is worth. Once the machinery to automate a job becomes cheaper than the worker, that worker is out of a job.
In the 1980s, the business owners (who never really like the New Deal) use their newfound leverage to create a coalition with libertarians and social conservatives to essentially dismember the government portion of the New Deal. Once this is done, the pie continues to grow, but the rich have start to grow their portion of it.