The Wuchang Uprising of October 10, 1911 started the Xinhai Revolution, which led to the collapse of the Qing Dynasty and the establishment of the Republic of China (ROC).
In 1900, the ruling Qing Dynasty created a modernized army called the "New Army". At the time, the city of Wuchang, on the Yangtze River in the province of Hubei, had the most modern military industry. It began manufacturing weapons and other military equipment for the New Army. Sun Yat-sen's revolutionary ideas extensively influenced the officers and soldiers of the New Army in Wuchang; many joined revolutionary organizations.
The uprising itself broke out by accident. Revolutionaries in the Russian concession of the city had been building bombs, one of which accidentally exploded. This led police to investigate, and they discovered lists of Literary Society members within the New Army. Facing arrest, and certain execution, they staged a coup. The local officials panicked and fled, and the army took over the city in less than a day. The revolutionaries then telegraphed the other provinces asking them to declare their independence. Within six weeks, fifteen provinces had seceded.
The revolt was still considered merely the latest in a series of mutinies that had occurred in southern China. It was widely expected to be put down quickly, and ended up having much larger implications only because the Qing dynasty delayed action against the rebellion, allowing provincial assemblies in many southern provinces to declare independence from the Qing and declare allegiance to the rebellion.
Sun Yat-sen himself played no direct part in the uprising. He was traveling in the United States, trying to drum up support from overseas Chinese. [During the actual revolt he was in San Francisco. There's a Bufano statue of him at Old Saint Mary's Square off California Street near Grant Avenue.] He found out about the uprising by reading a newspaper report in Denver, Colorado. Within the Revolutionary Alliance, Sun had favored an uprising in his native Guangdong, citing local anti-Manchu sentiment. Sun's rival within the Alliance, Huang Xing, had favored an uprising in central China and had been planning an uprising for late October. The revolutionary leaders were thus caught off guard, leaving the mutineers without a leader. Li Yuanhong was dragged from under his bed and forced at gunpoint to become the leader of the Rebellion, and went on to become the only man to ever serve twice as president of the republican government of Beijing.
Many Chinese had felt that the Qing dynasty had lost the mandate of heaven, and this may have contributed to the revolt. Natural disasters, such as fires and floods, are often considered portents, and the Yangtze had overflowed its banks in 1911; the revolting troops were situated near that river. Such a flood would have had a profound psychological impact on government officials, rebels, peasants, and other Chinese in the vicinity. The flood had killed 100,000 people.
The Qing government, led by the regent 2nd Prince Chun, failed to respond for a crucial few weeks. This gave the revolutionaries time to declare a provisional government. They were joined by other provincial assemblies. Within a month, representatives from the seceding provinces had met and declared a Republic of China. Sun returned to China on December 25, and though he was elected provisional president of the Republic of China by the representatives of the sixteen provisional assemblies (an act that angered Yuan Shikai), Sun Yat-sen was aware of Yuan Shikai's military power and so he supported an earlier deal that left Yuan in charge.
The date of the uprising, October 10, widely known as Double Ten Day (traditional Chinese: 雙十節), is celebrated as the National Day (traditional Chinese: 國慶日) of the Republic of China. It is one of the most important national holidays in Taiwan.
October 10 is not the National Day of the People's Republic of China, but there may also be memorial activities in mainland China, usually referring to the day as the Anniversary for the Wuchang Uprising (simplified Chinese: 武昌起义纪念日).
[When my brother Sherry (Sheridan) lived in Taiwan, I visited him for a few weeks and arrived on October 10th, 1977. Everyone thought Ten/Ten was very lucky. Imagine what they must think about this date last year: Ten/Ten/Ten! Of course, this year is the Centennial of the Revolution.]