800,000 people are trafficked across national borders, which does not include millions trafficked within their own countries. Approximately 80% of transnational victims are women and girls, and up to 50% are minors, reports the U.S. State Department in a 2008 study. While the majority of trafficking victims are women who are forced into prostitution (in which case the practice is called sex trafficking), victims also include men, women and children who are forced into manual labour. Because of the illegal nature of human trafficking, its extent is unknown. A U.S. government report, published in 2005, estimates that about 700,000 people worldwide are trafficked across borders each year. This figure does not include those who are trafficked internally. Another research effort revealed that roughly 1.5 million individuals are trafficked either internally or internationally each year, of which about 500,000 are sex trafficking victims. Abolitionism Slavery has existed, in one form or another, throughout recorded human history – as have, in various periods, movements to free large or distinct groups of slaves. In antiquity Ashoka, who ruled the Maurya Empire in the Indian subcontinent from 269 to 232 BCE, abolished the slave trade but not slavery. The Qin dynasty, which ruled China from 221 to 206 BC, abolished slavery and discouraged serfdom. However, many of its laws were overturned when the dynasty was overthrown. Slavery was again abolished by Wang Mang in China in 17 CE but was reinstituted after his assassination. Americas The Spanish colonization of the Americas sparked a discussion about the right to enslave Native Americans. A prominent critic of slavery in the Spanish New World colonies was the Spanish missionary and bishop, Bartolomé de las Casas, who was "the first to expose the oppression of indigenous peoples by Europeans in the Americas and to call for the abolition of slavery there." One of the first protests against slavery came from German and Dutch Quakers in Pennsylvania in 1688. In 1777, Vermont, at the time an independent nation, became the first portion of what would become the United States to abolish slavery. In the United States, all of the northern states had abolished slavery by 1804, with New Jersey being the last to act. Abolitionist pressure produced a series of small steps towards emancipation. After the Act Prohibiting Importation of Slaves went into effect on January 1, 1808, the importation of slaves into the United States was prohibited, but