Secondly, but along the same lines as the above explanation, is that the people writing history change as well

The social changes of the 1960s and 1970s brought many women historians into what had largely been a male dominated field and introduced new perspectives and told new stories that had previously been undiscovered (unfortunately, due to lack a of male interest) or ignored (unfortunately, due to a lack of male interest).

History was once written largely only through limited primary sources; letters, journals, diaries, and newspapers, and of course, secondary sources-what others had already written. But historians not so long ago began to "think outside the box," and by using sources such as estate

inventories, court documents, and even oral histories, these historians opened up a world of new information.

Locating new information of course changed how we saw events of the past, and only naturally new interpretations developed...and in this way one could say history changed.

Lastly, and related to the third, is that the availability of research sources have changed...largely through technology

All of this makes researching much easier and much less frustrating for the historian, and it allows him or her more time to make critical decisions, and to explore avenues that would not otherwise be considered.