3. A second cause of the civil war was _the different system of labor in the North and in the South_. In the former section the laborers were freemen; in the latter, slaves. In the South the theory was that capital should own labor; in the North that both labor and capital are free. In the beginning all the colonies had been slaveholding. In the Eastern and Middle States the system of slave-labor had been abolished. In the Northwestern Territory slavery was excluded from the beginning. Thus there came to be a dividing line drawn through the Union. Whenever the question of slavery was agitated, a sectional division would arise between the North and the South. The danger arising from this source was increased by several subordinate causes. 4. The first of these was the invention of the COTTON GIN to replace hand-labor in separating the fiber from the seeds of the cotton plant. It was invented in 1793 by Eli Whitney, of Massachusetts, and through its immediate adoption cotton suddenly became the most profitable of all the staples. In proportion to the increased profitableness of cotton, slave-labor grew in demand and slavery became an important and deep-rooted institution. 5. From this time onward, there was constant danger of disunion. In the MISSOURI AGITATION of 1820-21, threats of dissolving the Union were freely made in both the North and the South. When the Missouri Compromise was enacted, it was the hope of Mr. Clay and his fellow-statesmen to save the Union by removing the slavery question from politics. 6. Next came the NULLIFICATION ACTS of South Carolina. The Southern States had become cotton-producing; the Eastern States had given themselves to manufacturing. The tariff measures favored manufacturers at the expense of producers. Mr. Calhoun proposed to remedy the evil by annulling the laws of Congress; and another compromise was found necessary in order to allay the animosities which had been awakened. 7. The ANNEXATION OF TEXAS led to a renewal of the agitation. Those who opposed the Mexican War did so because of the fact that thereby slavery would be extended. Whether the territory acquired should be made into free or slaveholding States was the question next agitated. This led to the OMNIBUS BILL, by which the excitement was again allayed. 8. In 1854 the KANSAS-NEBRASKA BILL opened the question anew. Meanwhile, the character of the Northern and the Southern people had become quite different. In population and wealth the North had far outgrown the South. In 1860 Mr. Lincoln was elected by the votes of the Northern States. The people of the South were exasperated at the choice of a chief-magistrate whom they regarded as hostile to their interests. [Sidenote: Sectional Estrangement.]