Quakers in particular were early leaders in abolitionism. In 1688 Dutch Quakers in Germantown, Pennsylvania, sent an antislavery petition to the Monthly Meeting of Quakers. By 1727 British Quakers had expressed their official disapproval of the slave trade. Three Quaker abolitionists, Benjamin Lay, John Woolman, and Anthony Benezet, devoted their lives to the abolitionist effort from the 1730s to the 1760s, with Lay founding the Negro School in 1770, which would serve more than 250 pupils. In June 1783 a petition from the London Yearly Meeting and signed by over 300 Quakers was presented to Parliament protesting the slave trade. In 1787 the Society for Effecting the Abolition of the Slave Trade was formed, with 9 of the 12 founder members being Quakers. During the same year, William Wilberforce was persuaded to take up their cause; as an MP, Wilberforce was able to introduce a bill to abolish the slave trade. Wilberforce first attempted to abolish the trade in 1791, but could only muster half the necessary votes; however, after transferring his support to the Whigs, it became an election issue. Abolitionist pressure had changed popular opinion, and in the 1806 election enough abolitionists entered parliament for Wilberforce to be able to see the passing of the Slave Trade Act 1807. The Royal Navy subsequently declared that the slave trade was equal to piracy, the West Africa Squadron choosing to seize ships involved in the transfer of slaves and liberate the slaves on board, effectively crippling the transatlantic trade. Through abolitionist efforts, popular opinion continued to mount against slavery, and in 1833 slavery itself was outlawed throughout the British Empire (with exceptions)—at that time containing roughly 1/6 of the world's population (rising to 1/4 towards the end of the century). In the United States, the abolition movement faced much opposition. Bertram Wyatt-Brown notes that the appearance of the Christian abolitionist movement "with its religious ideology alarmed newsmen, politicians, and ordinary citizens. They angrily predicted the endangerment of secular democracy, the mongrelization, as it was called, of white society, and the destruction of the federal union. Speakers at huge rallies and editors of conservative papers in the North denounced these newcomers to radical reform as the same old 'church-and-state' zealots, who tried to shut down post offices, taverns, carriage companies, shops, and other public places on Sundays. Mob violence sometimes ensued." A postal campaign in 1835 by the American Anti-Slavery Society