Why did the United States seize Pacific Islands during ww2?

Four Japanese transports, hit by both U.S. surface vessels and aircraft, beached and burning at Tassafaronga, west of positions on Guadalcanal, on November 16, 1942. They were part of the huge force of auxiliary and combat vessels the enemy attempted to bring down from the north on November 13th and 14th. Only these four reached Guadalcanal. They were completely destroyed by aircraft, artillery and surface vessel guns. #

AP Photo

Following in the cover of a tank, American infantrymen secure an area on Bougainville, Solomon Islands, in March 1944, after Japanese forces infiltrated their lines during the night. #

AP Photo

Torpedoed Japanese destroyer Yamakaze, photographed through periscope of USS Nautilus, 25 June 1942. The Yamakaze sank within five minutes of being struck, there were no survivors. #

AP Photo/U.S. Navy

American reconnaissance patrol into the dense jungles of New Guinea, on December 18, 1942. Lt. Philip Winson had lost one of his boots while building a raft and he made a make-shift boot out of part of a ground sheet and straps from a pack. #

AP Photo/Ed Widdis

A helmeted Australian soldier, rifle in hand, looks out over a typical New Guinea landscape in the vicinity of Milne Bay on October 31, 1942, where an earlier Japanese attempt at invasion was defeated by the Australian defenders. #

AP Photo

On August 24, 1942, while operating off the coast of the Solomon Islands, the USS Enterprise suffered heavy attacks by Japanese bombers. Several direct hits on the flight deck killed 74 men; the photographer of this picture was reportedly among the dead. #

AP Photo

A breeches buoy is put into service to transfer from a U.S. destroyer to a cruiser survivors of a ship, November 14, 1942 which had been sunk in naval action against the Japanese off the Santa Cruz Islands in the South pacific on October 26. The American Navy turned back the Japanese in the battle but lost an aircraft carrier and a destroyer. #

AP Photo

Secondary batteries of an American cruiser formed this pattern of smoke rings as guns from the warship blasted at the Japanese on Makin Island in the Gilberts before U.S. forces invaded the atoll on November 20, 1943. #

AP Photo

Troops of the 165th infantry, New York's former "Fighting 69th" advance on Butaritari Beach, Makin Atoll, which already was blazing from naval bombardment which preceded on November 20, 1943. The American forces seized the Gilbert Island Atoll from the Japanese. #

AP Photo

U.S. Marines are seen as they advance against Japanese positions during the invasion at Tarawa atoll, Gilbert Islands, in this late November 1943 photo. Of the nearly 5,000 Japanese soldiers and workers on the island, only 146 were captured, the rest were killed. #

AP Photo

Infantrymen of Company "I" await the word to advance in pursuit of retreating Japanese forces on the Vella Lavella Island Front, in the Solomon Islands, on September 13, 1943. #

U.S. Army

Two of twelve U.S. A-20 Havoc light bombers on a mission against Kokas, Indonesia in July of 1943. The lower bomber was hit by anti-aircraft fire after dropping its bombs, and plunged into the sea, killing both crew members. #

USAF

Small Japanese craft flee from larger vessels during an American aerial attack on Tonolei Harbor, Japanese base on Bougainville Island, in the Central Solomon Islands on October 9, 1943. #

AP Photo/U.S. Navy

Two U.S. Marines direct flame throwers at Japanese defenses that block the way to Iwo Jima's Mount Suribachi on March 4, 1945. On the left is Pvt. Richard Klatt, of North Fond Dulac, Wisconsin, and on the right is PFC Wilfred Voegeli. #

AP Photo/U.S. Marine Corps

A member of a U.S. Marine patrol discovers this Japanese family hiding in a hillside cave, June 21, 1944, on Saipan. The mother, four children and a dog took shelter in the cave from the fierce fighting in the area during the U.S. invasion of the Mariana Islands. #

AP Photo

Columns of troop-packed LCIs (Landing Craft, Infantry) trail in the wake of a Coast Guard-manned LST (Landing Ship, Tank) en route to the invasion of Cape Sansapor, New Guinea in 1944. #

Photographer's Mate, 1st Cl. Harry R. Watson/U.S. Coast Guard

With its gunner visible in the back cockpit, this Japanese dive bomber, smoke streaming from the cowling, is headed for destruction in the water below after being shot down near Truk, Japanese stronghold in the Carolines, by a Navy PB4Y on July 2, 1944. Lieutenant Commander William Janeshek, pilot of the American plane, said the gunner acted as though he was about to bail out and then suddenly sat down and was still in the plane when it hit the water and exploded. #

AP Photo/U.S. Navy

As a rocket-firing LCI lays down a barrage on the already obscured beach on Peleliu, a wave of Alligators (LVTs, or Landing Vehicle Tracked) churn toward the defenses of the strategic island September 15, 1944. The amphibious tanks with turret-housed cannons went in in after heavy air and sea bombardment. Army and Marine assault units stormed ashore on Peleliu on September 15, and it was announced that organized resistance was almost entirely ended on September 27. #

AP Photo

Para-frag bombs fall toward a camouflaged Japanese Mitsubishi Ki-21, "Sally", during an attack by the US Army Fifth Air Force against Old Namlea airport on Buru Island, Dutch East Indies, on October 15, 1944. A few seconds after this picture was taken the aircraft was engulfed in flames. The design of the para-frag bomb enabled low flying bombing attacks to be carried out with higher accuracy. #

AP Photo

Gen. Douglas MacArthur, center, is accompanied by his officers and Sergio Osmena, president of the Philippines in exile, extreme left, as he wades ashore during landing operations at Leyte, Philippines, on October 20, 1944, after U.S. forces recaptured the beach of the Japanese-occupied island. #

AP Photo/U.S. Army

Smoke billows up from the Kowloon Docks and railroad yards after a surprise bombing attack on Hong Kong harbor by the U.S. Army 14th Air Force October 16, 1944. A Japanese fighter plane (left center) turns in a climb to attack the bombers. Between the Royal Navy yard, left, enemy vessels spout flames, and just outside the boat basin, foreground, another ship has been hit. #

AP Photo

Landing barges loaded with U.S. troops bound for the beaches of Leyte island, in October 1944, as American and Japanese fighter planes duel to the death overhead. The men aboard the crafts watch the dramatic battle in the sky as they approach the shore. #

AP Photo

This photo provided by former Kamikaze pilot Toshio Yoshitake, shows Yoshitake, right, and his fellow pilots, from left, Tetsuya Ueno, Koshiro Hayashi, Naoki Okagami and Takao Oi, as they pose together in front of a Zero fighter plane before taking off from the Imperial Army airstrip in Choshi, just east of Tokyo, on November 8, 1944. None of the 17 other pilots and flight instructors who flew with Yoshitake on that day survived. Yoshitake only survived because an American warplane shot him out of the air, he crash-landed and was rescued by Japanese soldiers. #

AP Photo

A Japanese kamikaze pilot in a damaged single-engine bomber, moments before striking the U.S. Aircraft Carrier USS Essex, off the Philippine Islands, on November 25, 1944. #

U.S. Navy

A closer view of the Japanese kamikaze aircraft, smoking from antiaircraft hits and veering slightly to left moments before slamming into the USS Essex on November 25, 1944. #

U.S. Navy

Aftermath of the November 25, 1943 kamikaze attack against the USS Essex. Fire-fighters and scattered fragments of the Japanese aircraft cover the flight deck. The plane struck the port edge of the flight deck, landing among planes fueled for takeoff, causing extensive damage, killing 15, and wounding 44. #

U.S. Navy

The battleship USS Pennsylvania, followed by three cruisers, moves in line into Lingayen Gulf preceding the landing on Luzon, in the Philippines, in January of 1945. #

U.S. Navy

U.S. Marines going ashore at Iwo Jima, a Japanese Island which was invaded on February 19, 1945. Photo made by a Naval Photographer, who flew over the armada of Navy and coast guard vessels in a Navy search plane. #

AP Photo

A U.S. Marine, killed by Japanese sniper fire, still holds his weapon as he lies in the black volcanic sand of Iwo Jima, on February 19, 1945, during the initial invasion on the island. In the background are the battleships of the U.S. fleet that made up the invasion task force. #

AP Photo

U.S. Marines of the 28th Regiment of the Fifth Division raise the American flag atop Mt. Suribachi, Iwo Jima, on February 23, 1945. The Battle of Iwo Jima was the costliest in Marine Corps history, with almost 7,000 Americans killed in 36 days of fighting. #

AP Photo/Joe Rosenthal

U.S. invasion forces establish a beachhead on Okinawa island, about 350 miles from the Japanese mainland, on April 13. 1945. Pouring out war supplies and military equipment, the landing crafts fill the sea to the horizon, in the distance, battleships of the U.S. fleet. #

AP Photo/U.S. Coast Guard

An attack on one of the caves connected to a three-tier blockhouse destroys the structure on the edge of Turkey Nob, giving a clear view of the beachhead toward the southwest on Iwo Jima, as U.S. Marines storm the island on April 2, 1945. #

AP Photo/W. Eugene Smith

The USS Santa Fe lies alongside the heavily listing USS Franklin to provide assistance after the aircraft carrier had been hit and set afire by a single Japanese dive bomber, during the Okinawa invasion, on March 19, 1945, off the coast of Honshu, Japan. More than 800 aboard were killed, with survivors frantically fighting fires and making enough repairs to save the ship. #

AP Photo

During a Japanese air raid on Yonton Airfield, Okinawa, Japan on April 28, 1945, the corsairs of the "Hell's Belles," Marine Corps Fighter Squadron are silhouetted against the sky by a lacework of anti-aircraft shells. #

AP Photo/U.S. Marine Corps