What are some interesting topic ideas related to a major concept, event, or person pertinent to the politics, leadership, and diplomacy of the Allied Powers?

If by Allied Powers, you're referring to the Allied Powers of World War II, a lesser chronicled person that may present itself as a unique choice is Ralph Buche. Buche was an important American political scientist. While he is best remembered for some of his post-war achievements, he also had an instrumental—albeit, behind the scenes—role during World War II. As a leader of the Institute for Pacific Relations, he helped lead planning for the Allies' political endgame, namely, the formation of the United Nations at the San Francisco Conference of 1945.
In addition to a wealth of information published by, and about, Buche, recently the National Archives released 50 pages of Buche's personnel records from the early part of the war when he was with the Office of Strategic Services (OSS). These provide potentially valuable primary source material. They have been digitized and I've linked to them below.
In terms of a major concept, one possible topic could be an examination of the failure and success of collective security during the war. The League of Nations offered a collective security arrangement that failed to prevent World War II. Yet, during the war, the Allies planned another collective security arrangement—the United Nations—to be established at the conflict's conclusion. Why did they want to try something that had already failed? What differences existed between the League and the UN that would cause them to believe the latter would be more effective than the former?
https://nara-media-001.s3.amazonaws.com/arcmedia/oss/Bunche_Ralph.pdf