i can't speak to ancient times but can say that neither the abolitionist nor civil rights movement can be described as non-violent accurately.

it's true that there were non-violent segments of these social movements but to truly capture the scope of folks working for these changes one has to include violent actors. it is contemporary white-washing by those uninterested in seeing similar social upheavals which emphasizes the non-violent aspects of these movements.

for abolitionist times look at John Brown and Harper's Ferry, or the Lowry Wars, or the Seminole Nation. also Harriet Tubman's biography is a lot more nuanced than elementary school textbooks would make her seem.

for civil rights times look at the Black Panther Party, the myriad of riots, including Newark, Watts, D.C., Chicago, Baltimore etc. Also look the rhetoric of people like Stokely Carmichael, H. Rap Brown, Frantz Fanon, and of course Malcom X.