The Battle of Midway took place from June 4 to June 7, 1942, six months after Pearl Harbor, and brought to an end a string of successes by the Japanese across the Pacific. During the battle, the U.S. Navy defeated a Japanese attack against Midway Atoll northwest of Hawaii, destroying four Japanese aircraft carriers and a heavy cruiser while losing a carrier and a destroyer.
The battle was a crushing defeat for the Japanese and is widely regarded as the most important naval battle of World War II. The battle permanently weakened the Japanese Navy, costing them more than 200 naval aviators. Strategically, it allowed the U.S. Navy to seize the initiative in the Pacific and go on the offensive.
The Japanese plan was to lure America’s few remaining carriers into a trap and sink them. The Japanese also intended to occupy Midway Atoll to extend Japan’s defensive perimeter farther from its home islands. This operation was considered preparatory for further attacks against Samoa, as well as the invasion of Hawaii.
Had the Japanese captured Midway, the northeastern Pacific Rim would have been essentially defenseless. Japanese success also would have removed the last capital ships in the U.S. Pacific Fleet, ensuring Japanese naval supremacy in the Pacific until perhaps late 1943. The Midway operation, like the attack on Pearl Harbor, was not part of a campaign for the conquest of the United States itself, but was aimed at eliminating the U.S. as a strategic Pacific power, and to force the U.S. to negotiate an end to the Pacific War.
(edited from Wikopedia)