[I mentioned some of these items a few years ago, but now my list is longer.]
I was exchanging reading recommendations with a friend and realized that
 there have been a few books in recent years that actually changed my 
mind regarding what I thought happened in history. I read a lot of 
disappointing books -- too shallow, too heavy, too incomplete -- but I 
generally enjoy revisionist historians, especially if they have a 
provocative thesis and ample evidence. If you want to buy one of these, the best place to look  is 
https://www.bookfinder.com/ So here's a short list:
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 in 
The Russian Origins of the First World War 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. See also his 
Russian Revolution, July 1914, and 
Stalin's War, which describes World War II from Stalin's viewpoint rather than the usual FDR/Churchill one.
Philip Zelikow's The Road Less Traveled
 persuaded me that leaders missed a chance to end the war in December 
1916 with a poorly staffed peace initiative by Woodrow Wilson that was 
undercut by Secretary Lansing and "Colonel" House.
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. 
World War II: James Lacey's The Washington War, a
 bureaucratic politics analysis of FDR's leadership, persuaded me that 
administrative and economic policies had as much to do with America's 
ultimate success as its military operations. Phillips Payson O'Brien's The Second Most Powerful Man in the World: The Life of Admiral William D. Leahy, Roosevelt's Chief of Staff persuaded me that Leahy was far more influential on FDR's war policy than General George Marshall. Jonathan Schneer's Ministers at War: Winston Churchill and His War Cabinet
 persuaded me that much of Britain's success was due to the way the 
cabinet worked together; Churchill dominated, but the cabinet mattered. 
Postwar American policy: 
Derek Leebaert's, Grand Improvisation: America Confronts the British Superpower, 1945-57, persuaded me that Britain hoodwinked America into doing what it wanted until the collapse at Suez. Samuel F. Wells, Jr.'s Fearing the Worst: How Korea Transformed the Cold War,
 convinced me that American misjudgments in the Korean war made the 
nuclear arms race with the USSR more likely. Serhii Plokhy's Nuclear Folly: A History of the Cuban Missile Crisis, persuaded me that JFK lied about his policies and we came dangerously close to a full-scale nuclear war.
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, 
This Vast Southern Empire: Slaveholders at the Helm of American Foreign Policy.
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'Shaughnessy's 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.