Who were the leading figures in the abolitionist movement in the United States in the decades leading up the Civil War?

Abolition movement refers to the activities of many
leaders and general population in in the eighteenth and nineteenth century against the
practice of slavery. In the United States this movement began prior to its Independence
war. Towards close of 17th century Quakers condemned slaver as immoral. In late 18th
century many leaders of of the American revolution, including Thomas Jefferson and
Patrick Henry, criticized the practice of slavery. American Colonization Society led
antislavery protests in early nineteenth century, and tried to send free slaves to
Liberia.

Aggressive opposition to slavery began to develop
in 1830's under leadership of persons like William Lloyd Garrison, Lucretia Mott, Lewis
Tappan, and Theodore Dwight Weld.

New, aggressive opponents
of slavery began to spring up in the North during the 1830's.  Their leaders included
William Lloyd Garrison, Lucretia Mott, Lewis Tappan, and Theodore Dwight Weld.  In 1831,
Garrison launched his newspaper, The Liberator, in which he
demanded immediate freedom for slaves.  An American Anti-slavery Society was founded in
1833. During the 1830's and 1840's, many free blacks, including such former slaves as
Frederick Douglass, Henry Highland Garnet, Harriet Tubman, and Sojourner Truth joined
the abolition movement. 

In 1840, when some of the leaders of
abolition movement entered politics and founded the Liberty Party.  James G. Birney, a
former slaveholder born in Kentucky, contested for the post of  president in 1840 and
1844.

By 1848, abolitionists became an important element
the American politics. In this process the differences developed between North and the
South over the Issue of slavery. To reduce this kind of tensions a group of act,
popularly called Compromise of 1850,  were passed by Congress. Theses acts included a
strict fugitive slave law that required Northerners to return escaped slaves to their
owners. This law was resisted by Northerners who disobeyed it and started the the
"underground railroad", a system of escape routes and housing for runaway slaves. In
this way the conflict over slavery continued.

Abraham
Lincoln, who was staunchly opposed to slavery won the 1860 presidential election. This
caused apprehension among  Southerners that he would take strong measures to end
slavery. Under such conditions the Southern started to consider secession as an option,
sowing the seed for the Civil War.