The Pacific War was primarily a war between the Empire of Japan and the United States of America. After the invasion of French Indochina in 1940, the Japanese intention was to pursue their military expansion in Southeast Asia, aiming the Dutch East Indies. The fear of an American reaction had a significant role in planning the attack on the U.S. Pacific Fleet.
By Emok, derivative work [CC BY-SA 3.0(http://creativecommons.org/licenses/by-sa/3.0/deed.en)], via Wikimedia Commons
On December 7, 1941, Japanese planes from six carriers launched their Attack on Pearl Harbor, aiming to annihilate the U.S. capital ships. The U.S. Navy's chance was that none of its carriers were at Pearl Harbor, and most battleships, although damaged in the aftermath of the raid, could be repaired later.
In the spring of 1942, the Empire of Japan was in full expansion, aiming Port Moresby, in New Guinea, and Tulagi, in the Solomon Islands. The U.S. Navy awaited the Japanese, having information based on decrypting the Japanese naval communications, which resulted in the Battle of the Coral Sea. Although the losses were relatively equal, the Japanese had been stopped, which was an American strategic victory.
The Battle of Midway, which took place in early June 1942, proved to be the turning point of the Pacific War. By attacking the American base at Midway, the Japanese sought a decisive battle to destroy the U.S. carriers. However, again, the information received by the Americans enabled them to prepare and attack at the right moment, the Imperial Japanese Navy losing four aircraft carriers, while the U.S. Navy only one.
After the victory of Midway, the United States took the initiative, invading the island of Guadalcanal in August 1942. The Battle of Guadalcanal was actually a series of several battles fought during six months, in which the Americans won the fighting on the island. Although the sea and air battles were more balanced than the land battles, the attrition affected more the Japanese, whose ability to replace the losses was lower. The repeated Japanese failures on land compelled them to withdraw from Guadalcanal in February 1943.
Then, the U.S. Navy began to apply a strategy called leapfrogging or island-hopping to approach Japan. The strategy provided the occupation of lightly defended islands and isolation of the most heavily fortified ones by submarine blockade and air attacks. There were two main directions of attack. One, under General Douglas MacArthur, from the Solomon Islands to the Philippines, and the second, led by Admiral Chester Nimitz, from the islands of the Central Pacific towards Japan. In November 1943, the U.S. military captured the island of Tarawa and in mid-1944, the Island of Saipan.
The Battle of the Philippine Sea, which was the most important naval battle after Midway, took place on 19/20 June 1944, the U.S. Navy winning a decisive victory thanks to the technological progress and improved training. The primary outcome was that the aircraft carrier force of the Imperial Japanese Navy would not recover until the end of the war.
The next milestone of the Pacific War was in October 1944, when the Battle of Leyte Gulf took place. The battle resulted in the Japanese failure to prevent the occupation of the Philippines by the Americans, Japan thus being cut off from the access to the natural resources of Southeast Asia. At the same time, the Imperial Japanese Navy lost most of its capital ships.
In the last phase of the Pacific War, the U.S. military approached the Japanese Home Islands to obtain bases closer to them, in anticipation of a possible invasion of Japan.
first half of 1945,
the Americans won the Battle of Iwo Jima, and then the Battle of Okinawa,
both characterized by a fierce Japanese defense, which made the conquest of these Japanese islands be obtained with a high price of human lives.
Finally, the Japanese surrender came in August 1945, mainly due to the shock produced by the nuclear bombing of Hiroshima and Nagasaki.