Adams was particularly zealous about his abolitionist stance. It is interesting to note that he was more defiant and clear about his stance on slavery than anything else during his presidency. There was little miscommunication about where he stood during slavery. At the emergence of the Missouri Compromise, Adams recognized that the issue of slavery vs. free states would tear apart the Union, as the nation could not possess both realities in it and be called "one nation under God." Additionally, Adams was intense about arguing that the issue of slavery and the proportions to which the issue had risen prior to 1860 was due, in part, to the Constitution. While the United States "had prohibited the international slave trade," it permitted it domestically under the Constitution. Adams' implication here is that this fundamental disconnect had to be addressed. It was also the basis of his argument to the Supreme Court as he argued for the slaves aboard the Amistad slave ship that had killed the captain in order to not enter the life of enslavement. Adams' thoughts about slavery were unique at the time for while politicians were either in support of it or looking to negotiate it away through popular sovereignty or advocating states' rights, Adams' said that the issue had to be called out as morally wrong and politically infeasible.