During the years of Japan's invasion of China but prior to the entrance of the European forces into a general World War, the American government under Franklin Roosevelt began putting pressure on the Hirohito military regime to cease all hostilities in China and southeast Asia. However, American forces did not officially enter the Asian theater of war until after the attack on Pearl Harbor on December 7th, 1941. In 1937 however, Japanese military forces attacked another American naval force, the gunboat USS Panay on the Yangtze River. In OTL the American people paid little attention to the event and the US government accepted the Japanese explanation of an accident in a warzone. However in TTL, the reaction will be far greater. The article will only focus on the Pacific theater of the World War.
Second Sino-Japanese War
In 1931, Japanese soldiers staged an event (an explosion on railroad tracks) in Manchuria and used this event as a pretext to the invasion of Manchuria. The next year, an agreement was settled that recognized the state in Manchuria and also demilitarized Shanghai. The League of Nations then started imposing economic sanctions on Japan and the United States began uselessly chastising the Japanese government for it's invasion. In 1933, Japan attacked the Great Wall and established the Tanggu Truce, adding more Chinese land to the Japanese empire and another buffer state as well. In mid-1937 Japanese forces launched a full-scale invasion of China by taking Beijing and the port city of Tianjan before deciding to fully commit to the war Chinese forces attampted to regain Shanghai, and forced the Japanese to commit over 200,000 troops to try and retake the city. In three months the Japanese held the city once more and moved on to take the National Capital at Nanking. On December 12th 1937, Japanese aviators bombed the US Navy gunboat Panay on the Yangtze River near Nanking. The next day, the news reached the American bases in the Philippines and then was relayed to the mainland. President Roosevelt then presented the nation and Congress with a speech, calling December 12th a "Date which will live in Infamy". The American people then called for immediate action against the Japanese government for a technical undeclared act of war.
Lead Up to War
In response to the attack on the Panay and the subsequent American reaction, the US government demands an apology and reparations be paid to all the families of the dead sailors. On December 15th, news of the atrocities being committed in Nanking reached the United States and raised an even greater uproar for the American government to repspond with greater force. Hirohito asserts that the bombing was an accident and that Japan owed nothing to America. On December 21st ,Roosevelt begins to discuss War plans with Admiral Chester Nimitz and General Douglas MacArthur for scenarios of attacks and counterattacks against Japan in the event of a war. Roosevelt then secures an act from Congress beginning the implementation of a trade embargo on Japan that restricted the sales of aviation gasoline, scrap metal and any other essential airplane parts. This reduces Japan's ability to grow its much needed air force and naval air squadrons, and reduces Japan's ability to control its imperial holdings. Meanwhile, President Roosevelt, while still not wanting to risk a major war but believing one will inevitably come, asks Congress to appropriate $100 million to build up and upgrade the Pacific naval fleet and to move the fleet from San Diego to Hawaii in order to better respond to any Japanese aggression. Nevertheless, Japan continues to advance into the inland portions of China and atrocities continue to take place in Nanking so much so that by mid-January 1938, over 300,000 civilians have been slaughtered. The after inland forces are defeated by heavy guerrilla fighting and mass bombing of cities is economically difficult due to the fuel and parts shortages, Japanese forces halt the advance into China to focus on seizing oil rich areas in the Pacific islands (namely areas off the Australian coast, the Dutch East Indies and the Philippines). Knowing that this will cause a war with the US, the Japanese prepare for a massive naval attack on major US naval bases using what remains of their strategic gasoline reserves. This attack is planned for three months, from February to April 1938 with the attack scheduled for June of 1938. By April, another aircraft carrier with 70 planes has been added to the already sizeable US Pacific Fleet thanks to the appropriations bill campaigned by Roosevelt bringing the total to four carriers.
The War Begins
On June 1st, 1938 Japanese forces began landing Imperial Army forces with naval support in the Philippines with the US naval forces in Manila being quickly bombarded into submission by the numerically superior Japanese Imperial Navy