World War II involved the mobilization of over 100 million military personnel, making it the most widespread war in history.

Covering the war as a photographer:

Yōnosuke Natori (名取 洋之助, Natori Yōnosuke, 1910-1962) was a Japanese photographer and editor.

Born in Tokyo on 3 September 1910, Natori studied at Keio normal school but upon graduation went with his mother to Munich, where he studied at a school of arts and crafts.

He became interested in photography and in 1931 obtained a Leica, later that year getting a contract to work as a photographer for Ullstein, which in 1933 sent him to Manchuria to cover the Mukden Incident.

After immediate hostilities there had ended, Natori went to Japan and set up the first Nihon Kōbō, and when that collapsed set up the second, working on its magazine Nippon.

He went to Berlin for the 1936 Olympics, and thence went directly to the US, getting some of his photographs taken there published by Life and in 1937 becoming the first Japanese photographer to be contracted to that magazine.

The Second Sino-Japanese War (July 7, 1937 to September 9, 1945) was a major war fought between China and Japan, both before and during World War II. It was the largest Asian war in the twentieth century.

Before 1937, China and Japan fought in small, localized engagements in so-called "incidents." Yet the two sides, for a variety of reasons, refrained from fighting a total war. The 1931 invasion of Manchuria by Japan is known as the "Mukden Incident".

The last of these incidents was the Marco Polo Bridge Incident of 1937, marking the official beginning of full scale war between the two countries.

The Battle of Iwo Jima

The invasion of Iwo Jima began at 02:00 on February 19, 1945, and continued to March 26, 1945. The battle was a major initiative of the Pacific Campaign of World War II. The U.S. invasion, known as Operation Detachment, was charged with the mission of capturing the airfields on the island which up until that time had harried U.S. bombing missions to Tokyo.

The battle was marked by some of the fiercest fighting of the War.

The battle was the first American attack on the Japanese Home Islands and the Imperial soldiers defended their positions tenaciously.

Of the 21,000 Japanese soldiers present at the beginning of the battle, over 20,000 were killed and only 216 taken prisoner.

On August 6, 1945, the nuclear weapon Little Boy was dropped on Hiroshima by the crew of the American B-29 bomber Enola Gay, directly killing an estimated 70,000 people.

By the end of the year, injury and radiation brought total casualties to 90,000-140,000.

Approximately 69% of the city's buildings were completely destroyed, and 6.6 percent severely damaged.

Research about the effects of the attack was restricted under Allied occupation, and information censored until the signing of the San Francisco Peace Treaty in 1951, restoring control to the Japanese.