It goes back further than that; the world did not simply wake up one morning and decide to replace the pound sterling with the dollar just for the sake of doing it. It happened because of Bretton Woods, in turn a result of the Great War demolishing all of continental Europe while leaving America untouched, ensuring a dominant US position for the next century. The value of the dollar has fallen precipitously since America began importing oil and left the gold standard (which itself ended Bretton Woods and consequently hurt many other national economies far more than Americas.)

To revisit an example I noted elsewhere, single income households were the American norm prior to the seventies, not because husbands brutally oppressed their wives, but because one income was sufficient and it generally made more sense for the stay at home parent to be the one whose body manufactured their infants food. Liberals and conservatives alike have yet to address that radical change: The former typically consider the notion of stay at home moms sexist; the latter simultaneously demand it and make it impossible. That is just one of many reasons this is a long standing and longer brewing problem. America has, for decades, wanted to rest on and still retain its laurels; the two are mutually exclusive, we refuse to acknowledge that and here we are with a deteriorating living standard everyone sees but for which no one wishes to be accountable. Some people are so deeply in denial that confronting them with reality provokes angry accusations of treason, but reality has a way of forcing confrontation on its own if ignored long enough.

Oh, and have no fear: History majors are in no danger of matching the earning power of engineers any time soon. Part of the problem is the notion that ANY degree entitles one to a high paying job, which is simply not true. It is a requirement for most managerial positions (and often ANY degree will do,) but simply having a job in ones field does not, in itself, ensure it will be well paid. History majors are more likely to find themselves simply MANAGING burger flippers than teaching history (about the only thing a history degree qualifies one to do; it is a very popular but unemployable major,) but unlikely to ever earn six figure salaries whatever they do.