Online reference resources include online dictionaries, encyclopedias, atlases, almanacs. These resources are helpful for reseach when you want to find information about topics, locate facts, and answer questions.
The SAGE Handbook of Governance by 
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The Concise Princeton Encyclopedia of American Political History by 
A Dictionary of 20th-Century Communism by 
The Oxford Handbook of the American Presidency by 
The Oxford Handbook of the History of Political Philosophy by 
The Palgrave Macmillan Dictionary of Diplomacy by