The primary cause of the Boxer Rebellion, which erupted in China from 1899 to 1901, was widespread resentment against foreign imperialism and Christian missionary activity. The Boxers, a secret society known as the "Righteous and Harmonious Fists," sought to expel foreign influence from China, believing that the presence of Westerners and Christians had led to social upheaval and economic exploitation. This nationalist movement quickly escalated into violent conflict, targeting both foreigners and Chinese Christians. The rebellion ultimately resulted in foreign intervention, leading to a brutal suppression and severe reparations imposed on the Qing government, further weakening China's sovereignty.