China launches simultaneous offensives in Ladakh and across the McMahon Line, igniting the Sino-Indian War.

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 17.4% of the world population. China spans the equivalent of five time zones and borders fourteen countries by land across an area of nearly 9.6 million square kilometers (3,700,000 sq mi), making it the third-largest country by land 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 country's capital, while Shanghai is its most populous city by urban area and largest financial center.

Ladakh is a region administered by India as a union territory and constitutes an eastern portion of the larger Kashmir region that has been the subject of a dispute between India and Pakistan since 1947 and India and China since 1959. Ladakh is bordered by the Tibet Autonomous Region to the east, the Indian state of Himachal Pradesh to the south, both the Indian-administered union territory of Jammu and Kashmir and the Pakistan-administered Gilgit-Baltistan to the west, and the southwest corner of Xinjiang across the Karakoram Pass in the far north. It extends from the Siachen Glacier in the Karakoram range to the north to the main Great Himalayas to the south. The eastern end, consisting of the uninhabited Aksai Chin plains, is claimed by the Indian Government as part of Ladakh, but has been under Chinese control.

The McMahon Line is the boundary between Tibet and British India as agreed in the maps and notes exchanged by the respective plenipotentiaries on 24–25 March 1914 at Delhi, as part of the 1914 Simla Convention. The line delimited the respective spheres of influence of the two countries in the eastern Himalayan region along northeast India and northern Burma (Myanmar), which were earlier undefined. The Republic of China was not a party to the McMahon Line agreement, but the line was part of the overall boundary of Tibet defined in the Simla Convention, initialled by all three parties and later repudiated by the government of China. The Indian part of the Line currently serves as the de facto boundary between China and India, although its legal status is disputed by the People's Republic of China. The Burmese part of the Line was renegotiated by the People's Republic of China and Myanmar.