Why is the McMahon Line disputed by India and China?

The dispute over the McMahon Line stems from fundamental disagreements regarding the legitimacy of the 1913–14 Shimla Convention.

India upholds the McMahon Line as the official boundary between Arunachal Pradesh and Tibet. Conversely, China refuses to recognize the line, characterizing it as a product of British imperialist aggression. China’s position is rooted in the argument that Tibet was an integral part of China and lacked the authority to enter into international treaties independently; therefore, it considers the agreement "decidedly illegal".1

Following the 1949 establishment of the People’s Republic of China, the government rejected various pre-1949 treaties, including the Shimla Convention. Today, China claims Arunachal Pradesh as its sovereign territory, referring to the region as "Zangnan" or "South Tibet," and periodically issues standardized Chinese names for locations within the state to assert its claims. India consistently rejects these actions, maintaining that Arunachal Pradesh is an integral part of its territory. These conflicting stances have led to persistent diplomatic friction and military standoffs.12