When the news of Jackson's course reached Washington, Congress engaged in a heated debate over his occupation of the forts of a friendly power. In defending himself Jackson wrote that the Secretary of War had given him full power to conduct the campaign in the manner which seemed best. Spain, he claimed, had failed to fulfil that article of the treaty by which she was bound to restrain the Florida Indians from hostilities. Popular feeling proved too strong for Congress to assert its privileges as the sole war-making power. Jackson was not even rebuked for his course. During all those months, Onis, the Spanish Minister, and Adams were in negotiation over a treaty, which was not ratified until two years later. Florida was to be ceded to the United States on a payment of $5,000,000, to be applied in satisfying the claims of American citizens against Spain. The Sabine River, instead of the Rio Grande, was made the dividing line between the United States and Spanish territory. The line was to run from the mouth of the Sabine to the 32d parallel, thence north to the Red River and along it to the 100th meridian, thence north to the Arkansas and along that river to its source on the 42d parallel, and thence west to the Pacific. War with Spain was thus averted.
While the Florida question was under consideration, there arose another far more momentous to America. Free labor in the North and slave labor in the South were brought squarely face to face. Slave labor was fast rising in value. The new lands of the lower Mississippi opened a vast field for the employment of slaves in the production of cotton, sugar and tobacco. It was believed the extension of slavery into that new territory would save it from gradual extinction. The interstate traffic in slaves was viewed with abhorrence by many leading men in the South. John Randolph, while upholding slavery, denounced the traffic that was carried on in the Southern plantations. On the other hand it was seen that compromise would be of little value if the North only was to be permitted to increase its power by the admission of new States. New slave States as well were demanded by the Southerners.
In March, the citizens of Missouri had asked permission to form a State constitution and to be admitted into the Union. It was tacitly understood that slavery might be carried into territory east of the Mississippi belonging originally to the existing slave States. But Louisiana, west of the Mississippi, belonged to the whole of the United States rather than to any one of the several States. The question now arose whether Congress should establish slavery anew in territory of the United States. The alternative was presented to the people of the North whether to submit to the demands of the South or to consent to a dissolution of the Union. Though represented by a majority in Congress, the Northern States were defeated after a long struggle. John Quincy Adams doubted if Congress, under the American Constitution, had the right to prohibit slavery in a territory where it already existed. "If a dissolution of the Union should result from the slave question," he wrote, "it is obvious that it must shortly afterward be followed by a universal emancipation of the slaves."