Asian and Pacific theatre of World War I in the context of "German New Guinea"

World War I, or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a global conflict between two coalitions: the Allies (or Entente) and the Central Powers. Major areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. The war saw important developments in weaponry including tanks, aircraft, artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, and 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

The causes of World War I included the rise of the German Empire and decline of the Ottoman Empire, which disturbed the long-standing balance of power in Europe, the exacerbation of imperial rivalries, and an arms race between the great powers. Growing tensions in the Balkans reached a breaking point on 28 June 1914 when Gavrilo Princip, a Bosnian Serb, assassinated Franz Ferdinand, the heir to the Austro-Hungarian throne. Austria-Hungary blamed Serbia, and declared war on 28 July. After Russia mobilised in Serbia's defence, Germany declared war on Russia and France, who had an alliance. The United Kingdom entered the war after Germany invaded Belgium, and the Ottoman Empire joined the Central Powers in November. Germany's strategy in 1914 was to quickly defeat France before transferring its forces to the east, but its advance was halted in September, and by the end of the year the Western Front consisted of a near-continuous line of trenches from the English Channel to Switzerland. The Eastern Front was more dynamic, but neither side gained a decisive advantage, despite costly offensives. Italy, Bulgaria, Romania, Greece and others entered the war from 1915 onward.

The colonial expansion of the Empire of Japan in the Western Pacific Ocean and East Asia began in 1895 with Japan's victory over the Chinese Qing dynasty in the First Sino-Japanese War. Subsequent victories over the Russian Empire (Russo-Japanese War of 1904-1905) and the German Empire (World War I) expanded Japanese rule. Taiwan came under Japanese control from 1895, Korea in 1905, Micronesia in 1914, Southern Sakhalin in 1905, several concessions in China from 1903 onwards, and the South Manchuria Railway from 1905. In 1931, Japan invaded Manchuria, resulting in the establishment of the puppet state of Manchukuo the following year; thereafter, Japan adopted a policy of founding and supporting puppet states in conquered regions. These conquered territories became the basis for what became known as the Greater East Asia Co-Prosperity Sphere from 1940. (The Co-Prosperity Sphere expanded to include much of China, Indo-China, Malaya, the Philippines, the East Indies, Burma and New Guinea by 1942.)

Including Mainland Japan, colonies, occupied territories, and puppet states, the Empire of Japan at its apex was one of the largest empires in history. The total amount of land under Japanese sovereignty reached 8,510,000 km (3,300,000 sq mi) in 1942. By 1943, it accounted for more than 20% of the world's population at the time, with 463 million people in its occupied regions and territories.

The siege of Tsingtao (German: Belagerung von Tsingtau; Japanese: 青島の戦い; simplified Chinese: 青岛战役; traditional Chinese: 青島戰役) was the attack on the German port of Qingdao (Tsingtao) from Jiaozhou Bay during World War I by Japan and the United Kingdom. The siege was waged against Imperial Germany between 27 August and 7 November 1914. The siege was the first encounter between Japanese and German forces, the first Anglo-Japanese operation of the war, and the only major land battle in the Asian and Pacific theatre during World War I.