Aksai Chin is administered by China as part of the Xinjiang Uygur Autonomous Region and Tibet Autonomous Region and claimed by India as part of the union territory of Ladakh.
Chinese and the Sikhs signed a treaty in September 1842, which stipulated no transgressions or interference in the other country’s frontier. The British defeat of the Sikhs in 1846 resulted in transfer of sovereignty over Ladakh to the British which was satisfied that a traditional border was recognised and defined by natural elements. Hence a largely undefined area –Aksai Chin- lay between Pangong Lake and Karakoram Pass.
H. Johnson, a civil servant with the Survey of India proposed the “Johnson Line” in 1865, which put Aksai Chin in Jammu and Kashmir. Then China did not control Xinjiang, so this line was never presented to the Chinese.