The abolitionists saw slavery as an abomination and an affliction on the United States, making it their goal to eradicate slave ownership. They sent petitions to Congress, ran for political office and inundated people of the South with anti-slavery literature.
<span>Speculation the others don't fit.</span>
The dark cloud was like a stain of darkness over the wide-open plain.
(Is that too advanced?)
There was a red stain on the boy's shirt as he stood in the grassy plain.
(That's a bit simpler.)