Historical dictionary of the Korean War
Main Ref DS918 .H536 1991
The Korean War: an encyclopedia
Main Ref DS918 .K5645 1995
Encyclopedia of the Korean War : a political, social, and military history
Main Ref DS918 .E53 2000
The Koreas : a global studies handbook
Main Ref DS902 .C65 2
Historical dictionary of North Korea
Main Ref DS933.7 .K55 2003
One good first step in research is to gather background information on your topic. Or, perhaps you have a few topics in mind and want to read a little bit about each one before making a choice. Reference sources, particularly the subject encyclopedias, are a good place to begin. They're terrific at laying out basic information about a topic: a chronicle of its history; current status; theory or philosophy; key people; and most importantly, a bibliography of additional sources.
Reference sources will vary depending on your specific topic. A selection is listed here.