Why did japan switch sides during World War 1?

Answer 1

Japan sided with the Entente powers in WWI because it was a great opportunity to pick off Germany's colonies in the Pacific free of charge. The Japanese picked up all of Germany's Pacific holdings at the Versailles Peace Conference, including the Marshall Islands, the Mariana Islands, and the Caroline Islands. The Marshalls and Marianas were to cost the US much blood in WWII, wresting them from the Japanese. These came to Japan as "mandated" territories under the League of Nations and were not supposed to be militarized, but Japan spent twenty years burrowing tunnels and pillboxes into these coral islands.

In WWII the Japanese sided with the axis because Germany was going to fight Japan's old rival, the Russians, who have a Pacific Coast. The Japanese and Russians had fought a war in 1905, and the Japanese hoped the Germans would keep the Russians too busy to interfere with Japanese conquests in Asia. (Germany hoped Japan might kick the Russians around again, like they did in 1905). Additionally the British and French had colonies in Asia, and a military presence there, and looked like they would be fighting Germany again. My enemy's enemy is my friend. After Germany overran France and installed the collaborationsist Vicky regime as the government of France, the Vichy government "invited" the Japanese to take over French Indochina, which included Vietnam. The Japanese got much more out of the alliance than the Germans and Italians did. 85% of US war effort went to Europe until Germany was defeated, meaning the war against Japan was run on a shoestring for most of the time.

Answer 2

... They didn't.

Japan was siding with the British in the First world war as they had had close ties with them ever since their forced opening up to the west by the Americans. This led to them naturally siding with the British in the first world war.

However, the Americans distrusted the Japanese and disliked how they had close ties with the British. Not to mention that the feeling of racial superiority of Caucasians over asians was dominant. Therefore in the treaty of versailles, the major european powers not only rejected Japans wish to insert a clause in about 'racial equality', but also left them with only a few small gains in the pacific, the major one being Shandong province (China), previously a German held territory which due to Chinese uproar (they had done nothing in the war and expected something in return) was returned to the Chinese after pressure on the Japanese.

Japan was not only frustrated by this lack of land they had gained (they had a large, growing population with not much land to feed or let the population live on), they were also in need of more land, and when the great depression hit, Japan was one of the countries hardest hit.

In the Washington Disarmament Conference, the Americans sought to limit Japanese power and destroy their ties with England. They set quotas of war ships of 5:5:3, America, Britain, Japan and intervened with communications between the two nations. This was successful in braking Japans ties with Britain and led to further resentment against the west by the Japanese.

Therefore, When Hitler's Nazi Germany and Mussolini's Fascist Italy were looking for Allies with the same type of military regime, they looked towards Japan.

The Americans, despite being the ones to force the opening of Japan, were scared by the progress that Japan had made in such a short time. Japans win in the Sino-Japanese war of 1898 (I think) led to America being even more cautious, as Japan was the major power in Asia now. All in all, the Americans felt threatened by having a strong nation nearby and wished to get rid of its ties to another strong nation (quite silly as Britain would have been able to constrain Japan and their aggressive policies, hence prevent their invasion of China and therefore the Second world war in the pacific).

Answer 3

Because Japan was Britain's ally since 1908.