As historian Christopher L. Brown put it, slavery "had never been on the agenda in a serious way before," but the Revolution "forced it to be a public question from there forward." In the first two decades after the American Revolution, state legislatures and individuals took actions to free slaves, in part based on revolutionary ideals. Northern states passed new constitutions that contained language about equal rights or specifically abolished slavery; some states, such as New York and New Jersey, where slavery was more widespread, passed laws by the end of the 18th century to abolish slavery by a gradual method. By 1804, all the northern states had passed laws outlawing slavery, either immediately or over time. In New York, the last slaves were freed in 1827. Indentured servitude (temporary slavery), which had been widespread in the colonies (Half the population of Philadelphia had once been bonded servants) dropped dramatically, and disappeared by 1800. An Act Prohibiting Importation of Slaves sailed through Congress with little opposition. President Thomas Jefferson supported it, and it went in effect on January 1, 1808. Benjamin Franklin and James Madison each helped found manumission societies. No southern state abolished slavery, but for a period individual owners could free their slaves by personal decision, often providing for manumission in wills but sometimes filing deeds or court papers to free individuals. Numerous slaveholders who freed their slaves cited revolutionary ideals in their documents; others freed slaves as a reward for service. Records also suggest that some slaveholders were freeing their own mixed-race children, born into slavery to slave mothers. The number of free blacks as a proportion of the black population in the upper South increased from less than 1 percent to nearly 10 percent between 1790 and 1810 as a result of these actions.