two more militia companies—one made up of Black members and the other of pardo (mixed race). Serving in the militia brought free Black men one step closer to equality with Whites, allowing them, for example, the right to carry arms and boosting their earning power. However, actually these privileges distanced free Black men from enslaved Blacks and encouraged them to identify with Whites. Slavery had been tacitly enshrined in the U.S. Constitution through provisions such as Article I, Section 2, Clause 3, commonly known as the 3/5 compromise. Because of Section 9, Clause 1, Congress was unable to pass an Act Prohibiting Importation of Slaves until 1807. Fugitive slave laws (derived from the Fugitive Slave Clause of the Constitution—Article IV, Section 2, Clause 3) were passed by Congress in 1793 and 1850, guaranteeing the right for a slaveholder to recover an escaped slave within the U.S. Slave owners, who viewed slaves as property, made it a federal crime to assist those who had escaped slavery or to interfere with their capture. Slavery, which by then meant almost exclusively Black people, was the most important political issue in the Antebellum United States, leading to one crisis after another. Among these were the Missouri Compromise, the Compromise of 1850, the Dred Scott decision, and John Brown's raid on Harpers Ferry. Prior to the Civil War, eight serving presidents owned slaves, a practice protected by the U.S. Constitution. By 1860, there were 3.5 to 4.4 million enslaved Black people in the U.S. due to the Atlantic slave trade, and another 488,000–500,000 Blacks lived free (with legislated limits) across the country. With legislated limits imposed upon them in addition to "unconquerable prejudice" from Whites according to Henry Clay, some Black people who were not enslaved left the U.S. for Liberia in West Africa. Liberia began as a settlement of the American Colonization Society (ACS) in 1821, with the abolitionist members of the ACS believing Blacks would face better chances for freedom and equality in Africa. The slaves not only constituted a large investment, they produced America's most valuable product and export: cotton. They not only helped build the U.S. Capitol, they built the White House and other District of Columbia buildings. (See Slavery in the District of Columbia.) Similar building projects existed in the slave states. By 1815, the domestic slave trade had become a major economic activity in the United States; it lasted