Dr. Labaree at USC has created a great summary of major international relations theories including definition and citation of the originating source. His IR LibGuide groups them alphabetically from Balance of Power to World-Systems analysis:
The databases below provide extensive coverage of political topics, including international relations, law, public administration and policy, international relations or trade, comparative politics, developing nations, etc. published in journals, books, public documents, web sites, and policy reports.
The History databases are quite useful for looking at past events in International Affairs, Political Sciences and Economics.
These history databases can limit to articles ABOUT a specific period of time (usually databases limit by publication date). Just put the dates of the time period in which you are interested in the ERA field.