Encyclopedias are great ways to get background information and understand the terms used to describe topics.
The Oxford encyclopedia of American cultural and intellectual history
Culture Wars
by
Roger Chapman (Editor)
Encyclopedia of Buddhism
Brill's encyclopedia of the religions of the indigenous people of South Asia
The encyclopaedia of Islam
Brill's encyclopedia of Sikhism
Routledge Encyclopedia of Ancient Mediterranean Religions
by
Eric Orlin (Editor)