Importation of slaves into the United States is banned... 1808

The United States Constitution, Article 1 Section 9 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.

In part, to ensure passage of such a law when the time came, the Pennsylvania Abolition Society was formed, and held its first meeting at the temporary Capital, Philadelphia, Pennsylvania, in 1794. On March 22, 1794, Congress passed the Slave Trade Act of 1794 that prohibited making, loading, outfitting, equipping, or dispatching of any ship to be used in the trade of slaves. 

Then on August 5, 1797, John Brown of Providence, Rhode Island was tried in federal court as the first American to be tried under the 1794 law. Brown was convicted and was forced to forfeit his ship Hope. On April 7, 1798, the fifth Congress passed an Act that imposed a three-hundred dollars per slave penalty on persons convicted of performing the illegal importation of slaves. It was an indication of the type of behavior and course of events soon to become commonplace in the Congress.

On Thursday, December 12, 1805, in the ninth Congress, Senator Stephen Row Bradley  of the State of Vermont gave notice that he should, on Monday next, move for leave to bring in a bill to prohibit the importation of certain persons therein described "into any port or place within the jurisdiction of the United States, from and after the first day of January," which will be "in the year of our Lord 1808." His words would be repeated many times by the legislators in the ninth Congress. The certain persons were described as being slaves on Monday, December 16, 1805.

Wary of offending the slaveholders to the least degree, the United States Senate amended the proposed Senatorial Act, then passed it to the House of Representatives whereat it became meticulously scrutinized and, figuratively, poked and prodded. Cautiously, ever mindful of not inciting the wrath of slaveholders, members of the House produced a bill which would explain the Senatorial Act. The two measures were bound together, with the House bill being called H R 77 and the Senate Act being called An Act to prohibit the importation of slaves into any port or place within the jurisdiction of the United States, from and after the first day of January, in the year of our Lord, 1808. The bound measure also regulated the coastwide slave trade. The bound measure was placed before President Thomas Jefferson on March 2, 1807 for his approbation. He signed the bill into law on March 3, 1807.

The 1807 Act of Congress was modified and supplemented by the fifteenth Congress. The importation of slaves into the United States was called "piracy" by an Act of Congress that punctuated the era of good feeling in 1819. Any citizen of the United States found guilty of such "piracy" might be given the death penalty. The role of the Navy was expanded to include patrols off the coasts of Cuba and South America. The effective date of the Act, January 1, 1808, was celebrated by Peter Williams Jr. in An Oration on the Abolition of the Slave Trade; delivered in the African Church in the City of New York, January 1, 1808.