Long ere this, all the Northern and Middle States had made provision for the emancipation of such slaves as remained within their borders, and only a few years previous (in 1829 and 1831-32) Virginia had made strong but insufficient efforts toward the same end. The failure to free Virginia of Slavery--the effort to accomplish which had been made by some of the greatest of her statesmen--only served to rivet the chains of human bondage more securely throughout all the Slave States, and from that time on, no serious agitation occurred in any one of them, looking toward even the most gradual emancipation. On the other hand, the advocates of the extension of the Slave-Power by the expansion of Slave-territory, were ever on the alert, they considered it of the last importance to maintain the balance of power between the Slave States and the Free States. Hence, while they had secured in 1819 the cession from Spain to the United States of the Slave-holding Floridas, and the organization of the Slave Territory of Florida in 1822--which subsequently came in as a Slave State under the same Act (1845) that admitted the Free State of Iowa--their greedy eyes were now cast upon the adjoining rich territories of Mexico. Efforts had (in 1827-1829) been made to purchase from Mexico the domain which was known as Texas. They had failed. But already a part of Texas had been settled by adventurous Americans under Mexican grants and otherwise; and General Sam Houston, an adherent of the Slave Power, having become a leading spirit among them, fomented a revolution. In March, 1836, Texas, under his guidance, proclaimed herself a Republic independent of Mexico.