| 200,000 in 1810. |
| 445,000 in 1820. |
| 965,000 in 1830. |
| 1,377,000 in 1840. |
Thus thirty years saw an increase of nearly seven-fold in the population of this region.[28]
Meanwhile, slavery had become the issue of the day. The slave power was in control of the Federal Government, and in order to maintain its authority, it needed new slave states to offset the free states that were being carved out of the Northwest.
Here were three forces—first the desire of the frontiersmen for "elbow room"; second the demand of King Cotton for unused land from which the extravagant plantation system might draw virgin fertility and third, the necessity that was pressing the South to add territory in order to hold its power. All three forces impelled towards the Southwest, and it was thither that population pressed in the years following 1820.
3. Texas
Mexico lay to the Southwest, and therefore Mexico became the object of American territorial ambitions. The district now known as Texas had constituted a part of the Louisiana Purchase (1803); had been ceded to Spain (1819); had been made the object of negotiations looking towards its purchase in 1826; had revolted against Mexico and been recognized as an independent state in 1835.
Texas had been settled by Americans who had secured the permission of the Mexican Government to colonize. These settlers made no effort to conceal their opposition to the Mexican Government, with which they were entirely out of sympathy. Many of them were seeking territory in which slavery might be perpetuated, and they introduced slaves into Texas in direct violation of the Mexican Constitution. The Americans did not go to Texas with any idea of becoming Mexican subjects; on the contrary, as soon as they felt themselves strong enough, they declared their independence of Mexico, and began negotiations for the annexation of Texas to the United States.
The Texan struggle for independence from Mexico was cordially welcomed in all parts of the United States, but particularly in the South. Despite the protests of Mexico, public meetings were held; funds were raised; volunteers were enlisted and equipped, and supplies and munitions were sent for the assistance of the Texans in ships openly fitted out in New Orleans.
No sooner had the Texans established a government than the campaign for annexation was begun. The advocates of annexation—principally Southerners—argued in favor of adding so rich and so logical a prize to the territory of the United States, citing the purchase of Louisiana and of Florida as precedents. Their opponents, first on constitutional grounds and then on grounds of public policy, argued against annexation.
Opinion in the South was greatly aroused. Despite the fact that many of her foremost statesmen were against annexation, some of the Southern newspapers even went so far as to threaten the dissolution of the Union if the treaty of ratification failed to pass the Senate.