Understanding the historical or societal context of many design elements can sometimes take extra work. Most of this factually based information will tend to be located in books. Here are some searches that might help you locate some of this information:
Chronology - what was happening at a certain point in time? Generally covers politics, war, culture, etc.
[Country name] Social Life and Customs
Berg Fashion Library * is an excellent resource to find articles about how fashion has been affected by history and society.
Oxford Art Online * allows one to search Grove Art, The Encyclopedia of Aesthetics, and several other excellent art reference resources. This is particularly helpful to locate background information surrounding a topic.