Why was the US able to acquire Florida from Spain in 1819?

At first, the annexing of Texas had been refused by the United States. In 1844, Sam Houston (the Texan President) signed a treaty of annexation with the US. Although the Senate yet again refused to ratify the treaty, for fear the annexation of Texas would cause war with Mexico. Houston refused to give up, and pressured the US by pretending Texas was going to ally itself with Britain. This trick worked, and in 1845, Congress passed a joint resolution admitting Texas to the Union.