The event that first appeared, among the ones offered, is the World War I in 1914, after the assassination of Archduke Ferdinand. The war began with the declaration of the war to Serbia by Austro-Hungary, due to which Russia entered the war by announcing the war to Austrio-Hungary. Already tired of the wars, and the failures with Japan, Russia entered the war under very big domestic problems. This situation was used by the Bolsheviks, and with the enormous dissatisfaction of the people, in a pair of Revolutions, took over the power in October 1917. The war ended with the defeat of Germany and its allies, by signing the Treaty of Versailles, according to which Germany was supposed to pay war compensation. Many countries suffered great damage during the war, many countries had a bad economic situation after the war, it was a great depression that used Mussolini to promote the ideas of fascism. The terms of the Treaty of Versailles have contributed to a bad economic situation in Germany, along with great depression, humiliation and a sense of helplessness, which used Hitler as the main arguments for the rise of fascism and Nazism.
World War I started in 1914. This war caused citizens to revolt and overthrow corrupt governments in areas like Russia, where the Bolshevik Revolution took place during 1917.
World War I ended with the Treaty of Versailles in 1919. This punished Germany for the beginning of World War I. Along with Germany, several other countries were destroyed. Not only was their infrastructure destroyed, their economy was suffering as well. This all helps lead to the rise of fascism.
Because it weakened the Japanese morale. The IJN would no longer be capable of operations in the Pacific Southwest because their resources were low. They were also still reeling from the losses at Midway.
The Americans secured Henderson field, a major airfield that prevented the Japanese from spreading south into Australia. The Aussies would be helpful in Operation D-Day.
US-Australian supply lines were no longer under threat. It's why the IJN tried to take the island in the first place.
