As the government of Tibet, China concluded several treaties (1876, 1886, 1890, 1893) with British India touching on the status, boundaries and access to Tibet. Chinese government sources consider this a sign of sovereignty rather than suzerainty.
The Indian government wished to revive its ancient friendly ties with China. When the PRC was declared, India was among the first countries to give it diplomatic recognition. After coming to power, the PRC announced that its army would be occupying Tibet.
In 1914, the Tibetan government signed the Simla Accord with Britain, ceding the South Tibet region to British India. The Chinese government denounced the agreement as illegal.
The Dogra–Tibetan War or Sino-Sikh War was fought from May 1841 to August 1842, between the forces of the Dogra nobleman Gulab Singh of Jammu, under the suzerainty of the Sikh Empire, and Tibet under the suzerainty of Qing China. Gulab Singh's commander was the able general Zorawar Singh Kahluria, who, after the conquest of Ladakh, attempted to extend its boundaries in order to control the trade routes into Ladakh.
A subsequent battle near Leh in 1842 led to a Tibetan defeat. The Treaty of Chushul was signed in 1842 maintaining the status quo ante bellum.