Slavery

Main article: John Quincy Adams and abolitionism

A longtime opponent of slavery, Adams used his new role in Congress to fight it, and he became the most prominent national leader opposing slavery.^[5][98] In 1836, Southern Representatives voted in a "gag rule" that immediately tabled any petitions about slavery, thus preventing any discussion or debate of the slavery issue. He became a forceful opponent of this rule and conceived a way around it, attacking slavery in the House for two weeks.^[5] The gag rule prevented him from bringing slavery petitions to the floor, but he brought one anyway. It was a petition from a Georgia citizen urging disunion due to the continuation of slavery in the South. Though he certainly did not support it and made that clear at the time, his intent was to antagonize the pro-slavery faction of Congress into an open fight on the matter.^[5] The plan worked.
The petition infuriated his Congressional enemies, many of whom were agitating for disunion themselves. They moved for his censure over the matter, enabling Adams to discuss slavery openly during his subsequent defense. Taking advantage of his right to defend himself, Adams delivered prepared and impromptu remarks against slavery and in favor of abolition.^[5] Knowing that he would probably be acquitted, he changed the focus from his own actions to those of the slaveholders, speaking against the slave trade and the ownership of slaves. He decided that if he were censured, he would merely resign, run for the office again, and probably win easily.^[5] When his opponents realized that they played into his political strategy, they tried to bury the censure. Adams made sure this did not happen, and the debate continued. He attacked slavery and slaveholders as immoral, and condemned the institution while calling for it to end.^[5] After two weeks, a vote was held, and he was not censured. He delighted in the misery he was inflicting on the slaveholders he so hated, and prided himself on being "obnoxious to the slave faction."^[5]
Although the censure of Adams over the slavery petition was ultimately abandoned, the House did address the issue of petitions from enslaved persons at a later time. Adams again argued that the right to petition was a universal right, granted by God, so that those in the weakest positions might always have recourse to those in the most powerful. Adams also called into question the actions of a House that would limit its own ability to debate and resolve questions internally. After this debate, the gag rule was ultimately retained.^[99] The discussion ignited by his actions and the attempts of others to quiet him raised questions of the right to petition, the right to legislative debate, and the morality of slavery.^[5] During the censure debate, Adams said that he took delight in the thought that southerners would forever remember him as "the acutest, the astutest, the archest enemy of southern slavery that ever existed."^[5]
In 1844, he chaired a committee for reform of the rules of Congress, and he used this opportunity to try once again to repeal the gag rule. He spent two months building support for this move, but due to northern opposition, the rule narrowly survived.^[5] He fiercely criticized northern Representatives and Senators, in particular Stephen A. Douglas, who seemed to cater to the slave faction in exchange for southern support.^[5] His opposition to slavery made him, along with Henry Clay, one of the leading opponents of Texas annexation and the Mexican–American War. He correctly predicted that both would contribute to civil war.^[5] After one of his reelection victories, he said that he must "bring about a day prophesied when slavery and war shall be banished from the face of the earth."^[5] He wrote in his private journal in 1820:^[100]

The discussion of this Missouri question has betrayed the secret of their souls. In the abstract they admit that slavery is an evil, they disclaim it, and cast it all upon the shoulder of…Great Britain. But when probed to the quick upon it, they show at the bottom of their souls pride and vainglory in their condition of masterdom. They look down upon the simplicity of a Yankee's manners, because he has no habits of overbearing like theirs and cannot treat negroes like dogs. It is among the evils of slavery that it taints the very sources of moral principle. It establishes false estimates of virtue and vice: for what can be more false and heartless than this doctrine which makes the first and holiest rights of humanity to depend upon the color of the skin?

In 1841, at the request of Lewis Tappan and Ellis Gray Loring, Adams joined the case of United States v. The Amistad. Adams went before the Supreme Court on behalf of African slaves who had revolted and seized the Spanish ship Amistad. Adams appeared on 24 February 1841, and spoke for four hours. His argument succeeded; the Court ruled in favor of the Africans, who were declared free and returned to their homes.^[101] Among his opponents was President Martin Van Buren. In the following years, the Spanish government continued to press the US for compensation for the ship and its cargo, including the slaves. Several southern lawmakers introduced Congressional resolutions to appropriate money for such payment, but none passed, despite support from Democratic presidents James K. Polk and James Buchanan.^{[citation needed]}
Adams continued to speak out against what he called the "Slave Power", that is the organized political power of the slave owners who dominated all the southern states and their representation in Congress.^[102] He vehemently attacked the annexation of Texas (1845) and the Mexican War (1846–48) as part of a "conspiracy" to extend slavery.^[103]