World War I: I'm now persuaded that Russia shares much of the blame for the start of the Great War by its policies to dominate Turkey and by mobilization during the July 1914 crisis. After deep dives into long-hidden Russian archives, Sean McMeekin showed that even Barbara Tuchman got the sequence wrong by relying on the falsified memoirs of the Russian Foreign Minister. McMeekin's books on Russian diplomacy and the July crisis changed my view of German war guilt, though Austria-Hungary still deserves shared blame with Russia.
FDR's boldness: I had long admired Franklin Roosevelt's strategic bravery in maneuvering the United States in support of Britain and against Hitler, believing that he was just ahead of public opinion, skillfully pulling it along. Lynne Olson''s Those Angry Days persuaded me that, much of the time, FDR vacillated, doing less than many of his advisors urged and hoped. He still was a great leader, just not quite as bold as I had thought.
Slave Power's influence on foreign policy: I never thought that slavery and its perpetuation had much impact on American foreign policy until I read Matthew Karp's eye-opening history. Karp details how the South dominated key foreign policy posts and consciously advocated policies to protect and even extend slavery in the decades before the War of the Rebellion. Defenders of slavery really had a "deep state."
The Revolutionary War: I used to have a typical American high school student's view of our war for independence as a story of brave patriots, toughened at Valley Forge and led by George Washington, who finally triumphed at Yorktown. Two books have changed my understanding of that conflict. One was Andrew Jackson O'Shaunessy's study of British politics during the conflict, The Men Who Lost America. He argues that the British gave up for broader strategic reasons. Add to this Holger Hoock's Scars of Independence, which describes the local violence on both sides and the mistreatment of Loyalists during and after the war. The good guys won, but they won dirty.