To better understand the war young American soldiers, seaman, and airmen like Roger were leaving home to join, it is helpful to have a basic idea of why it started and what had transpired before the US entered it.
Germany
There was a lot of bitterness on the part of Germany because they thought the Treaty of Versailles that ended WWI in 1919 was too punitive. It forbade Germany from rearming, and that had worked at first, but the financial pressures of the Great Depression, as well as political instability in Germany, helped bring on the rise of Hitler. When Hitler began building up the German military again, the US, Great Britain, and other European powers looked the other way and just let it happen.
Japan
Japan had its problems with the Treaty of Versailles as well. Its navy had been crucial during WWI in neutralizing Germany’s naval forces in the Pacific and capturing German holdings in China. As a comparatively small island, Japan’s problem has always been a lack of natural resources. Having seen decade upon decade of imperialism by Great Britain and the European countries, Japan greatly desired to have more influence in China and the rest of the Asian sphere. They certainly thought they should be able to take over all the Pacific holdings of Germany. Japan did receive an area called the “Japanese Mandate,” but large areas were also given to the US, Great Britain, the Netherlands, Australia, New Zealand, and France, which Japan thought it had earned.
Japan thought they should receive control of all the areas circled above after WWI. The National Interest / “Why Japan Turned Against the Paris Peace Treaty, and Why It Matters,” December 25, 1918
There was one other problem Japan had with the Treaty:
Even worse, Japanese delegates felt humiliated by their peers at Versailles. At one important juncture, Japan proposed a “racial equality clause” to guarantee equal treatment of foreign nationals regardless of race. When put to a vote, the clause gained majority support among the assembled diplomats. But sitting in the chair, U.S. President Woodrow Wilson ruled that the equality clause should not be included in the final agreement because unanimity had not been reached—the only instance during the entire Versailles conference that undivided consent was insisted upon.
Italy
Italy fought with the Allies in WWI, and was promised certain lands along its border with Austria-Hungary, islands in the Adriatic, portions of Albania and territory in the Ottoman Empire. Unfortunately, and in part because of Italy’s lackluster performance in the War, The Allies scaled back on what was awarded to Italy.
Just as anger and discontent in the wake of the Treaty of Versailles resulted in the rise of Hitler in Germany, Italian sentiment against it resulted in the rise of Mussolini, as well as growing resentment among the Italian people towards the Americans, the British and the French.