Currently, the entire Sino-Indian border is called the “Line of Actual Control” (LAC). This is an unusual term for an international boundary, so how did this concept arise and what does it mean?
Bluntly put, the term came from China’s tactics of encroaching into the Aksai Chin area of Ladakh. The Chinese surreptitiously built a road crossing the Northeastern corner of Aksai Chin between 1951-1957. And to defend it in depth, they began to move westward, gobbling more portions of the Aksai Chin plateau as they went along.
The Aksai Chin is a barren high-altitude desert where there is no habitation. Just who exercised sovereignty there and when was difficult to say.

