The 1807 act was a comprehensive attempt to close the slave trade. By passing the law in March, Congress gave all slave traders nine months to close down their operations in the United States. Article 1, Section 9 of the U.S. Constitution protected the slave trade for twenty years. Only starting January 1, 1808, could laws become effective to end the slave trade. “The Migration or Importation of such Persons as any of the States now existing shall think proper to admit, shall not be prohibited by the Congress prior to the Year one thousand eight hundred and eight, but a tax or duty may be imposed on such Importation, not exceeding ten dollars for each Person…” The ten sections of the 1807 act were designed to eliminate all American participation in the trade. Section 1 set the tone. After January 1, 1808, it would “not be lawful to import or bring into the United States or the territories thereof from any foreign kingdom, place, or country, any negro, mulatto, or person of colour, with intent to hold, sell, or dispose of such [person] … as a slave, to be held to service or labour.” The act provided an enormous penalty — up to $20,000 — for anyone building a ship for the trade or fitting out an existing ship to be used in the trade. The U.S. Congress passed this piece of landmark legislation to end the profitable international slave trade on March 2, 1807, and President Thomas Jefferson promptly signed the act, making it law. The act went into effect on January 1, 1808, prohibiting from that time on the importation of African slaves to the United States.
Basically since slaves trade was banned this meant the South didn't get to have more easy and cheap slaves. Also they had to keep their slaves alive. They will eventually keep the slaves for a long time and make them part of their everyday lives and economy. Tensions will rise between the Northern states and the Southern states leading to Civil War.