Japan invaded French Indonesia in 1940, leading FDR to embargoed the sale of all oil to Japan, with Great Britain following suit. This led to Japan invading other countries, like the Phllippines, in order to secure their natural resources
The only thing that could stop it continuing conquests was the US and its navy, which led to the plan to attack the US fleet stationed at Pearl Harbor.
Tojo, the Prime Minister, lobbied the emperor, Hirohito, to approve the plan, and eventually, he did.
At the Yalta conference, just before allied forces invade Germany, FDR, Stalin, and Churchill meet. They agree to give Manchuria to the USSR, and the USSR agrees to fight Japan. FDR thus consigns millions of European citizens of Soviet occupation–and several years earlier, to imprison thousands of American citizens of Japanese descent.
General MacArhur is forced to leave Manila, and US forces fight fierce battles on islands like Iwo Jima to create stations for the US Air Force to refuel planes to bomb Japan
In napalm bombing, US planes destroy 1/4 of Tokyo and kill 100,000 people, with 40,000 badly burned. This is repeated in other cities, but Japan refuses to surrender.
FDR dies, and Truman makes the decision to invade Japan. He’s also told about the atomic bomb. The USS Indianapolis is selected to carry the components of the bomb. But, it is torpedoed and sunk on its return trip. Sailors spend four days in the water and many are killed by sharks.
The bomb is dropped on Hiroshima, but Hirohito still refuses to surrender. In Los Alamos, Oppenheimer tells an audience, “My only regret is that we didn’t develop the bomb in time to use it against the Germans.”
The USSR invades Manchuria, which makes surrender inevitable. Even after Nagasaki three days later, they refused to consider surrender. Truman considered dropping a third bomb, on Tokyo. The day after, Japan offers terms, but they want Hirohito to retain power. Truman counter offers, but has to wait for three days for an answer.
In the meantime, the USSR has trapped the Imperial Army, which is vastly outnumbered. The USSR wins, but eventually, China retakes Manchuria from the Soviets.
Finally, four days after Japan’s first offer, and after more bombing of Tokyo, Hirohito agrees to unconditional surrender.
The Japanese treated prisoners atrociously. They prostituted women into “comfort women,”, beheaded many, starved them, amputated limbs without anesthetic, and infected them with diseases to study the reactions.
Tojo tried to commit suicide with a gun, but lived to be hanged. MacArthur was named to rebuild Japan, and did that successfully, but Truman thought MacArthur was egotistical and was building his own fiefdom. MacArthur was named Supreme Commander when North Korea invaded the south, and he recaptured Seoul. But, disobeying direct orders from Truman, he invaded China, and was relieved of command. There was a great public outcry and led to Truman deciding not to run for another term.