The Line of Actual Control (LAC) is the de facto border between India and China in the Himalayas — approximately 3,488 kilometres long and disputed along its entire length. Unlike a formal international boundary, the LAC has never been officially demarcated or agreed upon by both sides. India and China have different perceptions of where it runs in several sectors — most critically in Ladakh, Arunachal Pradesh, and Sikkim. The LAC became the defining crisis in India-China relations when Chinese troops crossed into Indian-claimed territory in the Galwan Valley in June 2020. The resulting clash — the first deadly confrontation between the two armies in 45 years — killed 20 Indian soldiers and an unknown number of Chinese troops. Galwan fundamentally altered India's strategic calculus. It accelerated India's defence modernisation, deepened its US partnership, and ended the assumption — prevalent in Indian policy circles since 2008 — that economic interdependence with China would prevent military conflict.