called on "advocates for American liberty" to oppose slavery, writing, "The plant of liberty is of so tender a nature that it cannot thrive long in the neighborhood of slavery.". The contradiction between calls for liberty and the continued existence of slavery also opened up the Patriots to charges of hypocrisy. In 1775, the English Tory writer Samuel Johnson asked, "How is it that we hear the loudest yelps for liberty among the drivers of negroes?" In the late 1760s and early 1770s, a number of colonies, including Massachusetts and Virginia, attempted to restrict the slave trade, but were prevented from doing so by royally appointed governors. In 1774, as part of a broader non-importation movement aimed at Britain, the Continental Congress called on all the colonies to ban the importation of slaves, and the colonies passed acts doing so. In 1775, the Quakers founded first antislavery society in the Western world, the Pennsylvania Abolition Society. 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. 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. Nevertheless, slavery continued in the South, where it became a "peculiar institution", setting the