U.S. Abolitionism

1688: Quakers in Germantown, PA author a petition against slavery to the Quaker church. 

1775: Pennsylvania Abolition Society formed in Philadelphia, the first abolition society within the territory that is now the United States of America.

1777: Constitution of the Vermont Republic partially banned slavery, freeing men over 21 and women older than 18 at the time of its passage. The ban was not strongly enforced.

1780: Pennsylvania passes An Act for the Gradual Abolition of Slavery, freeing future children of slaves. Those born prior to the Act remain enslaved for life. The Act becomes a model for other Northern states. Last slaves freed 1847.

1783: Massachusetts Supreme Judicial Court rules slavery unconstitutional, a decision based on the  
1780 Massachusetts constitution. All slaves are immediately freed.

1783: New Hampshire begins a gradual abolition of slavery.
 
1784: Connecticut begins a gradual abolition of slavery, freeing future children of slaves, and later all slaves.
 
1784: Rhode Island begins a gradual abolition of slavery.
 
1787: The United States in Congress Assembled passed the Northwest Ordinance of 1787, outlawing any new slavery in the Northwest Territories.
 
1794: The United States bans American ships from the trade and prohibits export by foreign ships in the Slave Trade Act.

1799: New York State passes gradual emancipation act freeing future children of slaves, and all slaves in 1827.

1800: The United States bans its citizens' investment and employment in the international slave trade in an additional Slave Trade Act.

1804: New Jersey begins a gradual abolition of slavery, freeing future children of slaves. Those born prior to the Act remain enslaved for life. The process later becomes complete with the ratification of the 13th Amendment in 1865.

1806: In a message to Congress, US President Thomas Jefferson calls for criminalizing the international slave trade, asking Congress to "withdraw the citizens of the United States from all further participation in those violations of human rights … which the morality, the reputation, and the best of our country have long been eager to proscribe."
 
1807 (March 2): The US makes international slave trade a felony in Act Prohibiting Importation of Slaves; this act takes effect on January 1, 1808.
 
1808: The US makes it a crime to import or export slaves.

1817: New York State sets a date of July 4 1827 to free all its ex-slaves from indenture.
 
1820: Compromise of 1820 in US prohibits slavery north of a line (36°30′).
 
1827: New York State abolishes last vestiges of slavery. Children born between 1799 and 1827 are indentured until age 25 (females) or age 28 (males).

1828: The Illinois Supreme Court in Phoebe v. Jay rules that indentured servants in Illinois cannot be treated as chattel and bequeathing them by will is illegal.

1845: The Illinois Supreme Court in Jarrot v. Jarrot frees the last indentured ex-slaves in Illinois who were born after the Northwest Ordinance.
 
1847: Indentured ex-slaves freed in Pennsylvania, thus freeing the last remaining ex-slaves, those born before 1780 (fewer than 100 in 1840 Census).
 
1850: In the United States, the Fugitive Slave Law of 1850 requires the return of escaped slaves to their owners.

1859: Trans-Atlantic slave trade completely ends.

1863:  Abraham Lincoln uses his wartime presidential powers to emancipate the slaves in states then in rebellion against the U.S. government.

1865:  The 13th Amendment to the U.S. Constitution is ratified on December 6 ending slavery in the U.S. except in Indian Territory (Oklahoma).  Slaves held by Indians are emancipated the following year.