This requires a subjective answer because the end of slavery was the result of the Union remaining intact by defeating the Confederacy. The anti slavery abolitionists had words and influence but they had no army. This is not meant as a funny remark by the way.
In my opinion as a student of US History, both when in high school, college and my interest in the War after that, the Abolitionists served to extend slavery. Here is why:
A. The Abolitionists tended to radicalize their position against slavery;
B. Politically speaking, because slavery had been a part of the Western Hemisphere for a few centuries, slavery was not a new issue;
C. With that fact in mind, I have read of no Abolitionist formula or planned way to free the slaves in the South without it causing a major political and economic disruption to the entire Union;
D. The Abolitionists had a strong "front man" in the person of the US President, Abraham Lincoln;
E. Lincoln had at least one plan to end slavery based on the plan Great Britain used in the West Indies;
F. The Abolitionist failed to see that their strongest supporter, Lincoln, had the correct agenda, which was to preserve the Union at all costs and take care of the slavery issue after that;
G. The Abolitionists' other positions ( in political terms, their bad baggage ) was their intolerance of non - Protestant religions, and the fact that they themselves wanted no slavery, but did not consider freed slaves to be equal with White Protestants; and
I. In my humble opinion, their radicalism, made Northerners less comfortable with the anti slavery movement.
The bottom line as I see it, is this: Without the Civil War, (which no sound mind wanted ) the radicalism of those radically opposed to slavery, injured the movement to abolish slavery in the United States.
abolitionists
abolitionists
The fought to end slavery
The abolitionists were members of the growing band of reformers who worked to abolish, or end, slavery.
The name of the reform group that worked to end slavery was the abolitionists. The abolitionist movement had leaders such as Frederick Douglass that worked to help free slaves.
Most of the abolitionists supported the Underground Railroad because most of the abolitionists wanted to end slavery.
Abolitionists wanted to end Slavery
An end to slavery.
Abolitionists
Abolitionists
Abolitionists believed that slavery was morally wrong and that it should be abolished. They advocated for the immediate end to slavery and the emancipation of enslaved individuals. Abolitionists played a crucial role in the movement to end slavery in the United States.
End slavery
abolitionists
abolitionists
The fought to end slavery
abolitionists
The end of slavery-