In the 1890s Britain and China were allies and Britain was principally concerned that Aksai Chin not fall into Russian hands.[7] In 1899, when China showed an interest in Aksai Chin, Britain proposed a revised boundary, initially suggested by George Macartney,[8] which put most of Aksai Chin in Chinese territory.[7] This border, along the Karakoram Mountains, was proposed and supported by British officials for a number of reasons. The Karakoram Mountains formed a natural boundary, which would set the British borders up to the Indus River watershed while leaving the Tarim River watershed in Chinese control, and Chinese control of this tract would present a further obstacle to Russian advance in Central Asia.[9] The British presented this line to the Chinese in a Note by Sir Claude MacDonald. The Chinese did not respond to the Note, and the British took that as Chinese acquiescence.[7] This line, known as the Macartney-MacDonald line, is approximately the same as the current Line of Actual Control.[7]
Both the Johnson-Ardagh and the Macartney-MacDonald lines were used on British maps of India.[7] Until at least 1908, the British took the Macdonald line to be the boundary,[13] but in 1911, the Xinhai Revolution resulted in the collapse of central power in China, and by the end of World War I, the British officially used the Johnson Line. However they took no steps to establish outposts or assert actual control on the ground.[8] In 1927, the line was adjusted again as the government of British India abandoned the Johnson line in favor of a line along the Karakoram range further south.[8] However, the maps were not updated and still showed the Johnson Line.[8]
When British officials learned of Soviet officials surveying the Aksai Chin for Sheng Shicai, warlord of Xinjiang in 1940-1941, they again advocated the Johnson Line.[7] At this point the British had still made no attempts to establish outposts or control over the Aksai Chin, nor was the issue ever discussed with the governments of China or Tibet, and the boundary remained undemarcated at India's independence.[7][8]