Qing China reached its largest extent during the 18th century, when it ruled China proper (eighteen provinces) as well as the areas of present-day Northeast China, Inner Mongolia, Outer Mongolia, Xinjiang and Tibet, at approximately 13 million km2 in size. There were originally 18 provinces, all of which in China proper, but later this number was increased to 22, with Manchuria and Xinjiang being divided or turned into provinces. Taiwan, originally part of Fujian province, became a province of its own in the late 19th century, but was ceded to the Empire of Japan in 1895 following the First Sino-Japanese War. In addition, many surrounding countries, such as Korea (Joseon dynasty), Vietnam frequently paid tribute to China during much of this period. Khanate of Kokand were forced to submit as protectorate and pay tribute to the Qing dynasty in China between 1774 and 1798.

What century did Qing China stretch to its largest?