During the period from 1820 to 1860, there was great expansion of the United States territory. Some strongly believed that slavery was the only cause of this growth. Opponents of the annexation of Texas and the Mexican war were the main supporters of this belief because they so strongly opposed the addition of a new slave state. Other factors, however, influenced the expansion that occurred during this time. These include the emigrants that were moving to Oregon, those who wanted to take California from Mexico, and those that wanted San Francisco itself.