How does a historian know if his information is relevant

If he finds evidence and can prove he is right

They were constantly being overlooked as a people and were being controlled by people who weren't really native to their homeland.

Several different things make up a culture like, how the people worship, their form of government, geography, and trade. religion is one of the most important things to a culture, it defines peoples life. their different beliefs form into festivities and events that merge with their culture. people that practice hinduism see cows as gods, so no doubt they would celebrate cows, and these celebrations would definitely merge with their culture. those that are buddhist live life trying to reach a certain level of peace, so no doubt would they change things in their life in order to correspond with their religion.