Republic of China (1912–1949) in the context of "Universal Postal Union"

Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main island of Taiwan, also known as Formosa, lies between the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the northeast, and the Philippines to the south. It has an area of 35,808 square kilometres (13,826 square miles), with mountain ranges dominating the eastern two-thirds and plains in the western third, where its highly urbanized population is concentrated. The combined territories under ROC control consist of 168 islands in total covering 36,193 square kilometres (13,974 square miles). The largest metropolitan area is formed by Taipei (the capital), New Taipei City, and Keelung. With around 23.9 million inhabitants, Taiwan is among the most densely populated countries.

Taiwan has been settled for at least 25,000 years. Ancestors of Taiwanese indigenous peoples settled the island around 6,000 years ago. In the 17th century, large-scale Han Chinese immigration began under Dutch colonial rule and continued under the Kingdom of Tungning, the first predominantly Han Chinese state in Taiwanese history. The island was annexed in 1683 by the Qing dynasty and ceded to the Empire of Japan in 1895. The Republic of China, which had overthrown the Qing in 1912 under the leadership of Sun Yat-sen, assumed control following the surrender of Japan in World War II. But with the loss of mainland China to the Communists in the Chinese Civil War, the government moved to Taiwan in 1949 under the Kuomintang (KMT).

China, officially the People's Republic of China (PRC), is a country in East Asia. With a population exceeding 1.4 billion, it is the second-most populous country after India, representing 17% of the world population. China borders fourteen countries by land across an area of 9.6 million square kilometers (3,700,000 sq mi), making it the third-largest country by area. The country is divided into 33 province-level divisions: 22 provinces, 5 autonomous regions, 4 municipalities, and 2 semi-autonomous special administrative regions. Beijing is the capital, while Shanghai is the most populous city by urban area and largest financial center.

China saw the first humans in the region arriving during the Paleolithic era. By the 2nd millennium BCE dynastic states had emerged in the Yellow River basin. The 8th–3rd centuries BCE saw a breakdown in the authority of the Zhou dynasty, accompanied by the emergence of administrative and military techniques, literature and philosophy. In 221 BCE, China was unified under an emperor, ushering in two millennia of imperial dynasties. With the invention of gunpowder and paper, the establishment of the Silk Road, and the Great Wall, Chinese culture flourished and has heavily influenced its neighbors and lands further afield. China began to cede parts of the country in the 19th century, to European powers by a series of unequal treaties. The 1911 Revolution overthrew the Qing dynasty and the Republic of China was established the following year. The country was unstable and fragmented during the Warlord Era, which ended upon the Northern Expedition conducted by the Kuomintang to reunify the country.

The Allies, formally referred to as the United Nations from 1942, were an international military coalition formed during World War II (1939–1945) to oppose the Axis powers. Its principal members were the "Big Four" – the United Kingdom, Soviet Union, United States, and China.

Membership in the Allies varied during the course of the war. When the conflict broke out on 1 September 1939, the Allied coalition consisted of the United Kingdom, France, and Poland, as well as their respective dependencies, such as British India. They were joined by the independent dominions of the British Commonwealth: Canada, Australia, New Zealand and South Africa. Consequently, the initial alliance resembled that of the First World War. As Axis forces began invading northern Europe and the Balkans, the Allies added the Netherlands, Belgium, Norway, Greece, and Yugoslavia. The Soviet Union, which initially had a nonaggression pact with Germany and participated in its invasion of Poland, joined the Allies after the German invasion of the Soviet Union in June 1941. The United States, while providing some material support to European Allies since September 1940, remained formally neutral until the Japanese attack on Pearl Harbor in December 1941, after which it declared war and officially joined the Allies. China had already been at war with Japan since 1937, and formally joined the Allies in December 1941.

Almost every country in the world participated in World War II. Most were neutral at the beginning, but relatively few nations remained neutral to the end. World War II pitted two alliances against each other, the Allies and the Axis powers. It is estimated that 74 million people died, with estimates ranging from 40 million to 90 million dead (including all genocide casualties). The main Axis powers were Nazi Germany, the Empire of Japan, and the Kingdom of Italy; while the United Kingdom, the United States, the Soviet Union and China were the "Big Four" Allied powers.

The countries involved in or affected by World War II are listed alphabetically, with a description of their role in the conflict.

World War II was the deadliest military conflict in history. An estimated total of 70–85 million deaths were caused by the conflict, representing about 3% of the estimated global population of 2.3 billion in 1940. Deaths directly caused by the war (including military and civilian fatalities) are estimated at 50–56 million, with an additional estimated 19–28 million deaths from war-related disease and famine. Civilian deaths totaled 50–55 million. Military deaths from all causes totaled 21–25 million, including deaths in captivity of about 5 million prisoners of war. More than half of the total number of casualties are accounted for by the dead of the Republic of China and of the Soviet Union. The following tables give a detailed country-by-country count of human losses.

Recent historical scholarship has shed new light on the topic of Second World War casualties. Research in Russia since the collapse of the Soviet Union has caused a revision of estimates of Soviet World War II fatalities. According to Russian government figures, USSR losses within postwar borders now stand at 26.6 million, including 8 to 9 million due to famine and disease. In August 2009 the Polish Institute of National Remembrance (IPN) researchers estimated Poland's dead at between 5.6 and 5.8 million. Historian Rüdiger Overmans of the Military History Research Office (Germany) published a study in 2000 estimating the German military dead and missing at 5.3 million, including 900,000 men conscripted from outside of Germany's 1937 borders, in Austria, and in east-central Europe. The Red Army claimed responsibility for the majority of Wehrmacht casualties during World War II. The People's Republic of China puts its war dead at 20 million, while the Japanese government puts its casualties due to the war at 3.1 million. An estimated 7–10 million people died in the Dutch, British, French and US colonies in South and Southeast Asia, mostly from war-related famine.

The causes of World War II have been given considerable attention by historians. The immediate precipitating event was the invasion of Poland by Nazi Germany on September 1, 1939, and the subsequent declarations of war on Germany made by Britain and France, but many other prior events have been suggested as ultimate causes. Primary themes in historical analysis of the war's origins include the political takeover of Germany in 1933 by Adolf Hitler and the Nazi Party; Japanese militarism against China, which led to the Japanese invasion of Manchuria and the Second Sino-Japanese War; Italian aggression against Ethiopia, which led to the Second Italo-Ethiopian War; or military uprising in Spain, which led to the Spanish Civil War.

During the interwar period, deep anger arose in the Weimar Republic over the conditions of the 1919 Treaty of Versailles, which punished Germany for its role in World War I with heavy financial reparations and severe limitations on its military that were intended to prevent it from becoming a military power again. The demilitarisation of the Rhineland, the prohibition of German unification with Austria, and the loss of its overseas colonies as well as some 12% of the pre-war land area and population of the metropole all provoked strong currents of revanchism in German politics.

Japan's Kwantung Army invaded the Manchuria region of China on 18 September 1931, immediately following the Mukden incident, a false flag event staged by Japanese military personnel as a pretext to invade. At the war's end in February 1932, the Japanese established the puppet state of Manchukuo. The occupation lasted until mid-August 1945, towards the end of the Second World War, in the face of an onslaught by the Soviet Union and Mongolia during the Manchurian Strategic Offensive Operation.

With the invasion having attracted great international attention, the League of Nations produced the Lytton Commission (headed by British politician Victor Bulwer-Lytton) to evaluate the situation, with the organization delivering its findings in October 1932. Its findings and recommendations that the Japanese puppet state of Manchukuo not be recognized and the return of Manchuria to Chinese sovereignty prompted the Japanese government to withdraw from the League entirely.

The Second Sino-Japanese War was fought between the Republic of China and the Empire of Japan between 1937 and 1945, following a period of war localized to Manchuria that started in 1931. It is considered part of World War II, and often regarded as the beginning of World War II in Asia. It was the largest Asian war in the 20th century. It is known in China as the War of Resistance Against Japanese Aggression.

On 18 September 1931, the Japanese staged the Mukden incident, a false flag event fabricated to justify their invasion of Manchuria and establishment of the puppet state of Manchukuo. This is sometimes marked as the beginning of the war. From 1931 to 1937, China and Japan engaged in skirmishes, including in Shanghai and in Northern China. Nationalist and Chinese Communist Party (CCP) forces, respectively led by Chiang Kai-shek and Mao Zedong, had fought each other in the Chinese Civil War since 1927. In late 1933, Chiang Kai-shek encircled the Chinese Communists in an attempt to finally destroy them, forcing the Communists into the Long March, resulting in the Communists losing around 90% of their men. As a Japanese invasion became imminent, Chiang still refused to form a united front before he was placed under house arrest by his subordinates who forced him to form the Second United Front in late 1936 in order to resist the Japanese invasion together.

The Qing dynasty (/tʃɪŋ/ CHING), officially the Great Qing, was a Manchu-led imperial dynasty of China and an early modern empire in East Asia. The last imperial dynasty in Chinese history, the Qing dynasty was preceded by the Ming dynasty and succeeded by the Republic of China. At its height of power, the empire stretched from the Sea of Japan in the east to the Pamir Mountains in the west, and from the Mongolian Plateau in the north to the South China Sea in the south. Originally emerging from the Later Jin dynasty founded in 1616 and proclaimed in Shenyang in 1636, the dynasty seized control of the Ming capital Beijing and North China in 1644, traditionally considered the start of the dynasty's rule. The dynasty lasted until the Xinhai Revolution of October 1911 led to the abdication of the last emperor in February 1912. The multi-ethnic Qing dynasty assembled the territorial base for modern China. The Qing controlled the most territory of any dynasty in Chinese history, and in 1790 represented the fourth-largest empire in world history to that point. With over 426 million citizens in 1907, it was the most populous country at the time.

Nurhaci, leader of the Jianzhou Jurchens and House of Aisin-Gioro who was also a vassal of the Ming dynasty, unified Jurchen clans (known later as Manchus) and founded the Later Jin dynasty in 1616, renouncing the Ming overlordship. As the founding Khan of the Manchu state he established the Eight Banners military system, and his son Hong Taiji was declared Emperor of the Great Qing in 1636. As Ming control disintegrated, peasant rebels captured Beijing as the short-lived Shun dynasty, but the Ming general Wu Sangui opened the Shanhai Pass to the Qing army, which defeated the rebels, seized the capital, and took over the government in 1644 under the Shunzhi Emperor and his prince regent. While the Qing became a Chinese empire, resistance from Ming rump regimes and the Revolt of the Three Feudatories delayed the complete conquest until 1683, which marked the beginning of the High Qing era. As an emperor of Manchu ethnic origin, the Kangxi Emperor (1661–1722) consolidated control, relished the role of a Confucian ruler, patronised Buddhism, encouraged scholarship, population and economic growth.

New Taipei City is a special municipality located in northern Taiwan. The city is home to an estimated population of 4,004,367 as of January 2023, making it the most populous city in Taiwan, and also the second largest special municipality by area, behind Kaohsiung. The top-level administrative divisions bordering New Taipei City are Keelung to the northeast, Yilan County to the southeast, and Taoyuan to the southwest, and it completely encloses the capital city of Taipei. Banqiao District is its municipal seat and biggest commercial area.

Before the establishment of Spanish and Dutch outposts in Tamsui in 1626, the area of present-day New Taipei City was mostly inhabited by Taiwanese indigenous peoples, mainly the Ketagalan people. From the late Qing era, the port of Tamsui was opened up to foreign traders as one of the treaty ports after the Qing dynasty of China signed the Treaty of Tientsin in June 1858. By the 1890s, the port of Tamsui accounted for 63 percent of the overall trade for entire Taiwan, port towns in the middle course of Tamsui River had also developed into bustling business and transportation centers. During the Japanese rule of Taiwan, the entire area of New Taipei City was organized as part of the Taihoku Prefecture. After the Republic of China took control of Taiwan in 1945, the present-day New Taipei City was designated on 7 January 1946 as Taipei County in Taiwan Province, which was constituted from the former Taihoku Prefecture, but not including present-day divisions of Taipei City, Keelung and Yilan County, the latter of which became detached from Taipei County on 10 October 1950. Its county status remained until 25 December 2010 when it was promoted to special municipal status and renamed as "New Taipei City".