Although the United States did not go to war against Japan until December 8, 1941, the day after Pearl Harbor, tensions between the two nations had been mounting for several years. Japan had been aggressively expanding its borders in Asia since the late 1930s. The United States Export Control Act of July 2, 1940 prohibited the export of basic war materials, which threatened Japan with supply shortages and damaged their trade. All trade between Japan and the United States stopped completely on July 27 , 1941, when President F. D. Roosevelt issued an Executive Order freezing all Japanese assets in the United States. Although Japan regarded this order as a hostile act, there were attempts at a peace settlement. The Japanese ambassador even relayed a reply to peace discussions to the Secretary of State one hour after the bombing of Pearl Harbor had begun.

Pearl Harbor

The Japanese sneak attack on the morning of December 7, 1941 severely crippled the United States' Pacific fleet and much of its air support. Three waves of Japanese planes destroyed three-fourths of the aircraft stationed at Pearl Harbor, and damaged all 8 battleships in the harbor. The Arizona was sunk and the Oklahoma capsized as American casualties were over 2300 men killed. This attack unified the American public. Decrying this "date which will live in infamy," President Roosevelt asked Congress to declare war on Japan. A joint session of Congress issued this declaration on December 8, 1941.

The Japanese Offensive

Carefully timed with the attack on Pearl Harbor was a series of Japanese offensives, planned by Admiral Yamamoto, against the countries and islands in the western and southwestern Pacific region. Guam and Wake Islands were captured on December 7, and the Japanese eventually claimed the Philippines, Hong Kong, parts of New Guinea and the Dutch East Indies, and threatened Australia. Not until mid-1942 was the Japanese expansion halted.

The American Response

Once the Japanese front was somewhat stabilized by American victories at Midway and Guadalcanal, American strategy evolved into a two-pronged thrust that would lead back to Japan. Attacks heading north from New Guinea and heading west across the central Pacific islands were planned, with the Allied forces converging in the Philippines. The heart of this strategy, devised in part by General Douglas MacArthur and Admiral Chester Nimitz, was island-hopping. Using a combination of air, land, and sea attacks, Allied forces would recapture Pacific islands and use the recovered territory as the launch base for the next series of attacks.

The Timeline
The sequence of dates below lists many of the major battles in the Pacific War.

1941 December 7 -- Pearl Harbor

1942 April -- Doolittle Raid

Named after the man who led it, this risky bombing run was the first American attack on the Japanese mainland. Of little strategic importance, it profoundly affected morale in both countries.

May -- Coral Sea
June -- Midway
July-November -- Guadalcanal

1943 saw island-hopping continue as the Americans moved toward Japan. Although progress was made, most Allied attention was focused on Europe and Hitler.
March -- Beginning of the Manhattan Project
March -- Bismarck Sea
The battle of Bismarck Sea was a US attack on a Japanese convoy bound for New Guinea with troops and supplies. An American victory, it forced Japan to curtail both the quantity and schedule of its reinforcements.
June August -- Aleutian Islands
November -- Gilbert Islands


1944

February -- Marshall Islands
February-June -- New Guinea
The New Guinea campaign drove out the Japanese after drawn-out fighting in the island jungles. It was an important preparatory step for the Allied invasion of the Philippines.
June -- Philippine Sea
June-August -- Marianas Islands
October -- Leyte Gulf, Philippines
The Battle of Leyte Gulf, part of the campaign to retake the Philippines, essentially destroyed the Japanese navy. Manilla fell in March 1945 as the Allies closed in on the Japanese mainland.


1945