The invasion of Tulagi, on 34 May 1942, was part of Operation Mo, the Empire of Japan's strategy in the South Pacific and South West Pacific Area in 1942. The plan called for Imperial Japanese Navy troops to capture Tulagi and nearby islands in the British Solomon Islands Protectorate. The occupation of Tulagi by the Japanese was intended to cover the flank of and provide reconnaissance support for Japanese forces that were advancing on Port Moresby in New Guinea, provide greater defensive depth for the major Japanese base at Rabaul, and serve as a base for Japanese forces to threaten and interdict the supply and communication routes between the United States and Australia and New Zealand.

Without the means to effectively resist the Japanese offensive in the Solomons, the British Resident Commissioner of the Solomon Islands protectorate and the few Australian troops assigned to defend Tulagi evacuated the island just before the Japanese forces arrived on 3 May. The next day, however, a U.S. aircraft carrier task force en route to resist the Japanese forces advancing on Port Moresby (later taking part in the Battle of the Coral Sea) struck the Japanese Tulagi landing force in an air attack, destroying or damaging several of the Japanese ships and aircraft involved in the landing operation. Nevertheless, the Japanese troops successfully occupied Tulagi and began the construction of a small naval base.

Over the next several months, the Japanese established a naval refueling, communications, and seaplane reconnaissance base on Tulagi and the nearby islets of Gavutu and Tanambogo, and in July 1942 began to build a large airfield on nearby Guadalcanal. The Japanese activities on Tulagi and Guadalcanal were observed by Allied reconnaissance aircraft, as well as by Australian coastwatcher personnel stationed in the area. Because these activities threatened the Allied supply and communication lines in the South Pacific, Allied forces counter-attacked with landings of their own on Guadalcanal and Tulagi on 7 August 1942, initiating the critical Guadalcanal campaign and a series of combined arms battles between Allied and Japanese forces that, along with the New Guinea campaign, decided the course of the war in the South Pacific.

The Empire of Japan was a historical nation-state and great power that existed from the Meiji Restoration in 1868 until the enactment of the post-World War II 1947 constitution and subsequent formation of modern Japan. It encompassed the Japanese archipelago and several colonies, protectorates, mandates, and other territories.

Under the slogans of fukoku kyōhei and shokusan kōgyō, Japan underwent a period of industrialization and militarization, the Meiji Restoration being the fastest modernisation of any country to date, all of these aspects contributed to Japan's emergence as a great power and the establishment of a colonial empire following the First Sino-Japanese War, the Boxer Rebellion, the Russo-Japanese War, and World War I. Economic and political turmoil in the 1920s, including the Great Depression, led to the rise of militarism, nationalism and totalitarianism as embodied in the Showa Statism ideology, eventually culminating in Japan's membership in the Axis alliance and the conquest of a large part of the Asia-Pacific in World War II.Japan's armed forces initially achieved large-scale military successes during the Second Sino-Japanese War (1937–1945) and the Pacific War. However, starting from 1942, particularly after the Battles of Midway and Guadalcanal, Japan was forced to adopt a defensive stance, and the American island hopping campaign meant that Japan was slowly losing all of the territory it had gained, and eventually, the Americans captured Iwo Jima and Okinawa Island, leaving the Japanese mainland completely unprotected. The U.S. forces had planned an invasion, but Japan surrendered following the atomic bombings of Hiroshima and Nagasaki and the nearly simultaneous Soviet declaration of war on August 9, 1945, and subsequent invasion of Manchuria and other territories. The Pacific War officially came to a close on September 2, 1945. A period of occupation by the Allies followed. In 1947, with American involvement, a new constitution was enacted, officially bringing the Empire of Japan to an end, and Japan's Imperial Army was replaced with the Japan Self-Defense Forces. Occupation and reconstruction continued until 1952, eventually forming the current constitutional monarchy known as Japan.

The Empire of Japan had three emperors, although it came to an end partway through Shōwa's reign. The emperors were given posthumous names, and the emperors are as follows: Meiji, Taisho, and Shōwa.