What lead to WWII and what were the consequences?

The main cause of World War Two was the aggressive military expansion of the two strongest Axis Powers: Germany and Japan.
Adolf Hitler and his Nazi political party came to power in Germany in 1933. Hitler had campaigned on a series of issues, including strengthening the German economy and regaining the lands lost by Germany at the end of World War One. Hitler advocated for what he called “Lebensraum” or living space; he believed that Germany should expand and include all German-speakers. Hitler envisioned a Germany that included most of Eastern Europe and parts of the Soviet Union. In 1939, the German army invaded Poland. France and Great Britain then declared war on Germany. By mid-1940, Germany had conquered most of mainland Europe.
Hideki Tojo, a leading general of the Japanese Army and later Prime Minister of Japan, wanted his country to expand militarily in order to become the dominant power in Asia and the Pacific. Due to the islands small stature, Japan needed more room for its population to expand, as well as more access to natural resources. Japan invaded Manchuria in 1937 and invaded many other Asian nations across the Pacific. By doing so, Japan came into conflict with the British, French, and Dutch empires. As it expanded its authority across the Pacific, Japan’s relationship with the United States became increasingly tense. On December 7th, 1941, Japan attacked the U.S. naval base at Pearl Harbor, Hawaii. The next day, the U.S. declared war on Japan.
As a result of their military expansion, Germany and Japan eventually came into conflict with the United States, the British Empire, France, the Soviet Union, and China (also known as the Allied Powers). After many hard-fought battles and campaigns in Europe, Asia, and North Africa, the Allies defeated the Axis Powers; Germany surrendered in April 1945 and Japan followed in August 1945. Both nations were militarily occupied by the Allied Powers after their surrender.