Himachal Day is observed in the Indian state of Himachal Pradesh every April 15. This official holiday commemorates the integration of 28 petty princely states into the Chief Commissioner's Province of Himachal Pradesh in 1948. The region has a rich history, having been inhabited since prehistoric times and influenced by various powers, including the Gurkhas and the British. During World War I, many local rulers supported the British, contributing to the war effort. Following India's independence in 1947, the hill states were consolidated, leading to the establishment of Himachal Pradesh. The day is distinct from Statehood Day, which celebrates the state's transition to full statehood in 1971.