what specific events helped to make slavery an...

[foxyrymekitty2004]

...issue of public debate?

[myt-LuBU]

The treatment of the slaves is what started it. All the lynchings, raping 10 y/o girls and women, molesting the children. Most of the time it was the upholders of the law that where doing the worst of it. That's something you can't hide for too long.

[Marion]

The inclusion of Missouri and Kansas into the Union, and the ensuing debate over whether they would be slave states or not.