The war in the Pacific really started with the Great Depression, which was a worldwide economic slump. Japan was affected in a big way as well: Exports fell by almost one third, and unemployment rose by almost one quarter.
Japan needed oil and coal to fuel its industries. It needed its machines to produce things it could sell to other countries to make money to buy food. Japan's leaders decided to use force if necessary to get this needed oil and coal.
In 1931, Japan invaded Manchuria, a province of China, to get more oil and coal. The League of Nations, a sort of not-too-powerful United Nations, told Japan to leave Manchuria. Japan refused and, further, left the League of Nations.
Japanese troops occupied Manchuria for another decade before expanding their occupation to a large part of China. Meanwhile, Germany and Italy were dominating discussions in Europe and in America. Italy had invaded Ethiopia, Germany had annexed Austria, and both countries had fought in the Spanish Civil War by 1939.
When Germany invaded Poland on September 1, 1939, Britain and France declared war on Germany. The attention of the world was on Europe. And as the Axis Powers (as Germany and Italy were called) conquered country after country, European nations and the United States paid little attention to Japan in the Far East.
Social Studies for Kids