Interesting. I see where you are going with this. Being an outspoken abolitionist in the 1820's was indeed quite radical. But he didn't really try to fundamentally change the system.
Actually, in a sort of extreme irony, maybe the arch-imperialist Teddy Roosevelt was the first?
Lincoln is also a candidate, but considering he didn't come around until the country was ready to end slavery by force, he probably doesn't qualify.
I mainly say JQA because he notoriously alienated everybody he knew in his quest for progress, and ultimately failed.
