When in 1819 Missouri applied for admission to the Union with a state constitution permitting slavery, there was a prolonged debate over the whole question, not only in Congress but throughout the entire country. North and South were distinctly pitted against each other with rival systems of labor. The following year Congress passed a law providing for the admission of Missouri, but, to restore the balance, Maine was separated from Massachusetts and was admitted to the Union as a State. It was further enacted that slavery should be forever prohibited from all territory of the United States north of the parallel 36 degrees 30', that is, north of the southern boundary of Missouri. It is this part of the act which is known as the Missouri Compromise. It was accepted as a permanent limitation of the institution of slavery. By this act Mason and Dixon's Line was extended through the Louisiana Purchase. As the western boundary was then defined, slavery could still be extended into Arkansas and into a part of what is now Oklahoma, while a great empire to the northwest was reserved for the formation of free States. Arkansas became a slave State in 1836 and Michigan was admitted as a free State in the following year. With the admission of Arkansas and Michigan, thirteen slave States were balanced by a like number of free States. The South still had Florida, which would in time become a slave State. Against this single Territory there was an immense region to the northwest, equal in area to all the slave States combined, which, according to the Ordinance of 1787 and the Missouri Compromise, had been consecrated to freedom. Foreseeing this condition, a few Southern planters began a movement for the extension of territory to the south and west immediately after the adoption of the Missouri Compromise. When Arkansas was admitted in 1836, there was a prospect of the immediate annexation of Texas as a slave State. This did not take place until nine years later, but the propaganda, the object of which was the extension of slave territory, could not be maintained by those who contended that slavery was a curse to the country. Virginia, therefore, and other border slave States, as they became committed to the policy of expansion, ceased to tolerate official public utterances against slavery.