This added enormously to the acrimony of the slavery controversy. There had from the beginning been accepted in the country a half formulated theory of the necessity of maintaining a "balance of power" between the opposing systems of slavery and free labor so far at least as the Senate, representing the states as such without regard to population, was concerned. From the beginning slave and free states had been admitted to the Union in effect in couples. Thus Vermont, admitted in 1791, was balanced by Kentucky, admitted in 1792. Tennessee came in in 1796 with no free state comrade till 1803, when Ohio was admitted. Louisiana, admitted in 1812, was offset by Indiana which became a state in 1816. Mississippi was admitted in 1817 and Illinois in the following year. Alabama, admitted in 1819, was balanced by Maine in 1820. Missouri came in in 1821 by a compromise that more than offset the omission to create a corresponding and compensatory free state. But when Arkansas was admitted in 1836, Michigan was thrown into the other scale in 1837. Florida and Texas, annexed in 1845, were balanced by Iowa in 1846 and Wisconsin in 1848. But for California as a free state there was no peopled region that could be carved into a compensatory slave state and for that reason, as well as because of the rise of the anti-slavery agitation to fever heat, the controversy about 1850 took on an angrier tone than ever, and one more seriously threatening to the Union. The people of the country at that time might justly have been divided into three classes, viz: 1. Those extreme opponents of slavery who were ready and eager to sacrifice the Union itself and the Constitution to the accomplishment of their emancipating purpose; 2. Those extreme pro-slavery men who were equally ready to wreck the Union in order to perpetuate and extend the system of slave labor; 3. Those intense lovers of the Union, North and South, who were ready to put aside and sacrifice their convictions for or against slavery in order to save the Nation from disruption with all its horrible consequences of civil war.