Actually there were repeated incidents of violence against blacks and republican officials who some racist groups felt were not 'their' officials because part of their electorate was newly freed black men. Murder, riots, lynchings, burning down buildings were common in this period. If it had been done today the entire south would have been an militarized occupied zone. You guys really should read up on the Reconstruction. The KKK started out as a social club for ex Confederate soldiers. Get it? They were the same people. Getting what they couldn't get by military force by terrorism against a civilian population. And no the freedman weren't obligated to arm themselves to the teeth and kill any white man who disses them. That's what civilization is supposed to be about. Unfortunately the federal government failed to act. The OP wanted to know what it would take for the Reconstruction to have succeeded. Given the behavior of the south it would have had to have been pretty drastic as I said.