Sutter's empire began to disintegrate when he decided to back the unpopular Alta Californian governor Manuel Micheltorena, who was soon overthrown by Alvarado and José Castro in an 1841 coup d'état. Sutter was jailed as a result, but not before Micheltorena issued the Sobrante Grant, which added of land to New Helvetian territory. In 1845, Castro arrived at Sutter's Fort and offered a deal to purchase New Helvetia; Sutter declined, although he later expressed regret for not accepting Castro's terms. In 1846, the Bear Flag Revolt was initiated by Americans in Sonoma who were frightened by growing Mexican hostility towards foreign presences in the region; taking the city by surprise, general Mariano Vallejo was captured at his headquarters in the city, and the irregular force demanded use of Sutter's prison facilities to host captured Mexican officials. Agreeing reluctantly, Sutter raised the Bear Flag over his fortification. However, he treated the Vallejos, whom he considered friends, as guests and not as prisoners. While the "Bear Flaggers" under William B. Ide and John C. Frémont continued to wage war against the Mexican government, Sutter attempted to resume a state of normalcy in New Helvetia, although the lack of manpower as a result of the revolt left productivity lagging.