If you ask most people who was the president of USA in World War 2, they’ll shout "FDR" before you even finish the sentence. They aren't wrong. Franklin Delano Roosevelt is the face of the American war effort, the man with the cigarette holder and the fireside chats who stared down the Great Depression and then took on the Axis powers. But here is the thing: he didn't actually finish the job.
History is messy. It doesn't always fit into those neat little boxes we learn in fifth grade. While FDR led the country through the vast majority of the conflict, he died just months before the final surrenders were signed. This left a relatively unknown haberdasher from Missouri named Harry S. Truman to make the most harrowing decisions in human history.
So, the "who" in this question is a duo. It’s a story of a transition of power in the middle of a global apocalypse.
FDR: The Architect of the War Effort
Roosevelt was elected to a record-breaking four terms, but his third and fourth terms were entirely consumed by the looming threat and eventual reality of global combat. When the Japanese bombed Pearl Harbor on December 7, 1941, FDR was already a seasoned crisis manager. He had spent years trying to nudge a reluctant, isolationist America toward helping the Allies via programs like Lend-Lease.
Honestly, Roosevelt’s biggest contribution wasn't just military strategy; it was industrial. He turned the United States into the "Arsenal of Democracy." He knew that the war wouldn't just be won by bravado on the front lines, but by the sheer volume of tanks, planes, and bullets rolling off assembly lines in Detroit and Pittsburgh.
By 1944, the man was exhausted. He was suffering from uncontrolled hypertension and congestive heart failure, secrets kept closely guarded by the White House. Yet, he ran for a fourth term because he felt he couldn't leave the ship in the middle of the storm. He won, but he looked like a ghost of his former self at the Yalta Conference, where he sat across from Winston Churchill and Joseph Stalin to carve up the post-war world.
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Roosevelt died on April 12, 1945, at his retreat in Warm Springs, Georgia. He had a massive cerebral hemorrhage. He never saw the victory in Europe. He never saw the end of the Pacific war. He left the world’s most powerful nation in the hands of a man who didn't even know the atomic bomb existed until he took the oath of office.
Harry S. Truman: The Man Who Had to Finish It
Imagine being Harry Truman. You've been Vice President for eighty-two days. You’ve barely spoken to the President. Then, suddenly, Eleanor Roosevelt tells you that "the President is dead," and when you ask if there is anything you can do for her, she looks at you and says, "Is there anything we can do for you? For you are the one in trouble now."
Truman was the president of USA in World War 2 during its most violent and controversial crescendo. He was the one who had to navigate the collapse of Nazi Germany in May 1945. More importantly, he was the one who faced the "impossible" choice regarding the invasion of Japan.
Military planners were telling him that a land invasion of the Japanese home islands could cost hundreds of thousands of American lives. Maybe millions. Truman was briefed on the Manhattan Project—the secret development of the atomic bomb—shortly after taking office. He wasn't a philosopher or a king; he was a pragmatic politician who viewed the bomb as a tool to end the slaughter as quickly as possible.
The Atomic Decision and the End of the War
When we look at the timeline, Truman's presidency is a whirlwind of world-changing events packed into just a few months:
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- May 8, 1945: VE Day (Victory in Europe).
- July 1945: The Potsdam Conference, where he faced off against Stalin.
- August 6 and 9, 1945: The dropping of atomic bombs on Hiroshima and Nagasaki.
- September 2, 1945: The formal surrender of Japan aboard the USS Missouri.
It’s easy to forget how much of the "World War 2 President" identity Truman actually earned in such a short window. He presided over the birth of the United Nations. He had to deal with the immediate aftermath of the Holocaust and the looming shadow of the Cold War.
Why the Distinction Matters
You can't talk about the American presidency in WWII without acknowledging the contrast between these two men. Roosevelt was an aristocrat, a charismatic orator, and a man of grand visions. Truman was plain-spoken, decisive, and often bluntly honest.
Roosevelt built the machine. Truman pushed the final buttons.
Some historians argue that Roosevelt’s more trusting nature toward Stalin might have led to a different Cold War outcome, while Truman’s "tough guy" stance set the stage for decades of nuclear standoff. It’s one of those great "what-ifs" of history. If FDR had lived another six months, would he have used the atomic bomb? Most biographers, like Doris Kearns Goodwin or David McCullough, suggest that yes, he likely would have, but we will never know for sure.
What You Should Take Away From This
When you're researching who was the president of USA in World War 2 for a test, a project, or just to settle a bar bet, remember the "Roosevelt-Truman" handoff.
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Roosevelt served from March 1933 to April 1945.
Truman served from April 1945 to January 1953.
The war lasted from 1939 to 1945 (with the U.S. involved from late '41). This means Roosevelt handled about 90% of the American involvement, while Truman handled the final 10%—which happened to be the most explosive 10% in the history of warfare.
Actionable Next Steps for History Buffs
If you want to go deeper than just a name and a date, here is how you can actually master this topic:
- Read the primary sources: Look up the "Infamy Speech" by FDR and compare its tone to Truman’s announcement of the Hiroshima bombing. The shift from "defensive outrage" to "solemn power" is palpable.
- Visit the digital archives: The FDR Presidential Library and the Harry S. Truman Library both have incredible digitized collections of their personal diaries and telegrams from the war years.
- Study the 1944 Election: It’s fascinating to see how the Democratic party basically forced Truman onto the ticket because they knew Roosevelt was dying, even if the public didn't.
- Understand the "Big Three": Remember that for most of the war, the world was run by Roosevelt, Churchill, and Stalin. By the end, it was Truman, Attlee, and Stalin. That shift changed the trajectory of the 20th century.
The story of the presidency in WWII isn't just about one man in a wheelchair; it's about the peaceful transfer of power in the middle of total war—a feat that is arguably as impressive as the military victory itself.