The subject filter can be helpful. Look for "International relations" or "Political Science." The Library Catalog filter is the best way to limit your results to books. Books are a great way to gain a sense of scope for a topic (instead of just piecing together very specific articles).
Use this for historical topics. Add terms like "foreign relations," "international relations," "diplomacy." or terms for specific events to help narrow your results.
Political Handbook of the World
The Oxford Handbook of Peaceful Change in International Relations
A World of Nations: the International Order since 1945 by 
Great Power Diplomacy by 
