In 1768, after ten years of preparation, siege, and attack, Kathmandu fell to Gorkha on the day of the festival of Indra and the Virgin Goddess. Prithvi Narayan died in 1775 and was succeeded by his son Bahadur Shah. The new Shah rulers, transferring their seat of power to Kathmandu after its conquest, undertook to expand and consolidate their territory. But in 1790, their troops met Chinese resistance while marching to Tibet, then a vassal of China. The 70,000 Chinese troops pushed the Gorkhas back into Nepal and defeat. The treaty stipulated that Nepal send the Chinese emperor a tribute every five years. This was done all the way up to 1912. After World War II, many changes were taking place. Colonies were gaining independence, particularly India from Great Britain. The Communists of China invaded Tibet, forcing many refugees to flee to Nepal and India.