Well, there’s a few ways this can go. But fortunately there are plenty of examples in history within our country and others (think Apartheid South Africa) where tyranny has been defeated without resorting to full fledged civil war. I suggest you read up on the activism of Desmond Tutu.
Also, this “putting down of peaceful protesters” is unquestionably bad and the department needs to be held to account, but it’s nowhere near the worst abuse by authorities in our country’s history (nobody got shot, no firehoses or dogs) and we’ve generally been able to eventually make progress in these kinds of situations (arc of history bends toward justice and all that) without resorting to massive bloodshed. If you look at a video like this and get mad, that’s good. It might motivate you to get active in your community and to let your government representatives know that they need fix this if they want to keep their jobs. But if your reaction is “that situation would have been much improved if people had defended themselves from those tyrants with lethal force” I really have to disagree.