When did the anti-slavery movement seriously take off ?

African slavery began in North America in 1619 at Jamestown, Virginia. The first American-built slave ship, Desire, launched from Massachusetts in 1636, beginning the slave trade between Britain’s American colonies and Africa. From the beginning, some white colonists were uncomfortable with the notion of slavery. At the time of the American Revolution against the English Crown, Delaware (1776) and Virginia (1778) prohibited importation of African slaves; Vermont became the first of the 13 colonies to abolish slavery (1777); Rhode Island prohibited taking slaves from the colony (1778); and Pennsylvania began gradual emancipation in 1780.

The Maryland Society for Promoting the Abolition of Slavery and the Relief of Free Negroes and Others Unlawfully Held in Bondage was founded in 1789, the same year the former colonies replaced their Articles of Confederation with the new Constitution, “in order to form a more perfect union.”

When the U.S. Constitution was written, it made no specific mention of slavery, but it provided for the return of fugitives (which encompassed criminals, indentured servants and slaves). It allowed each slave within a state to be counted as three-fifths of a person for the purpose of determining population and representation in the House of Representatives (Article I, Section 3, says representation and direct taxation will be determined based on the number of “free persons, including those bound to service for a term of years, and excluding Indians not taxed, three-fifths of all other persons.”)

The Constitution prohibited importation of slaves, to begin in 1808, but again managed to do so without using the words “slave” or “slavery.” Slave trading became a capital offense in 1819. There existed a general feeling that slavery would gradually pass away. Improvements in technology—the cotton gin and sewing machine—increased the demand for slave labor, however, in order to produce more cotton in Southern states. By the 1830s, many Southerners had shifted from, “Slavery is a necessary evil,” to “Slavery is a positive good.” The institution existed because it was “God’s will,” a Christian duty to lift the African out of barbarism while still exerting control over his “animal passions.”

The first leaders of the campaign, which took place from about 1830 to 1870, mimicked some of the same tactics British abolitionists had used to end slavery in Great Britain in the 1830s

Explanation:

they died because of a disease during the first spanish colonies.

this isn't a question and if you're going to list things be kind and use commas.