From about the 1960's ( my guess) on, American history began to include a more diverse set of narratives from minorities ect. What was/is the theory behind that? History behind it? Kind of the who/what/when/where/ and how of the situation.

I ask because I was asked why we don't have an assimilative history, a kind of AMERICAN history, and instead had various X studies, and cultural diversity history, and I didn't the complete background on why diversity studies were created.

Partly it's the impact of the civil rights movement and the GI Bill--an influx of middle- and working-class historians and a reappraisal of the roots of the country altered what most considered "our" history. Marxism is another somewhat long-term influence, though an actual Marxist school of history never really developed in the US the way it did in Europe; more often, working-class narratives were written in an effort to dull the edge of Marxism in the US or critique popular narratives of class conflict.

My naive guess is that it simply has to do with a social movement that accepted the influence and importance of minorities as a normative element of our history. It is "obvious" to us today that the histories of say black or hispanic or native american people are integral parts of the broader question of US history, but there was a time where the "white lens" if you will permit the expression was more common.

More common? More like exclusive. It's taken over 2000 years (in Western culture as a whole) to break free of the mostly Thucydidean paradigm of history = the State, war, diplomacy, and not much else. The decisions of the powerful were what defined "history." Regular people were not seen as contributing much to the process.

ding ding ding! I can't really say a defining moment where ''social histories'' started to pop up, somewhere around the 19th century they start to pop up more frequently. ''Marxian'' histories started poping up since the 19th century, before karl marx oddly enough - see the plethora of books called ''history of the dutch people, history of the french people...''

The major shift in history that came about in the 1960's are

a)carbon dating. This confirms that some society's were much older then expected.

b)a NEUTRAL point of view on religion. The 19th century histories were VERY anti-religious(Gibbon's&Michelet), while the previous one were very PRO religion. The 60's brought a very much needed neutrality on church. People started looking at religion as an influence, whether good or bad, but they did not see religion as the starting point of their culture(see african-american's)

c)Print culture and literacy starts to climb dramatically in what used to be illiterate social strata's.

d)The end of classical education as a whole - with more and more objects and techniques attributed to pre greco-roman culture, many social groups figured it's possible that their heritage is more then a tribal one.

The rise of postmodernism is the answer.

Postmodernism basically emphasizes plurality and that there is no absolute objective truth. Everyone’s perceptions and beliefs are equally valid. It tries to look beyond traditional authority and power structures. Postmodernism became very popular after WWII for obvious reasons. It became even more influential in historical scholarship as the new generation of historians trained post-WWII came to dominate historical scholarship starting in the 1960s. Thus, new types of history were written that emphasized plurality over the history of state, male-dominated authority (so-called “traditional” political narratives). Women’s history is just as important as men’s history. African-American as important as white. Working class as important as elite. So forth and so on.

All of which is, of course, a load of crap.

...makes sense, given your name and your undertitle