I had a horse that literally almost killed an older mare of mine. It was an odd situation but she was closed in the run-in and he was in the stall. He broke down the stall door and started attacking her. We woke up to hearing banging, we thought someone was knocking on our door. It was my horse kicking at the wall in the barn. There were holes in the wall, etc and my mare was seriously injured. She wasn't in the greatest shape to begin with.
MY method to fixing this, because he would viciously attack other horses regularly. I put him out to pasture with 2 very dominate Belgians, who gave him a good whoopin. He never attacked another horse again, he was still dominate, just not vicious.
I don't recommend doing what I did, I wouldn't even do that now. I was like 13 and didn't know any better.
BUT my point to that is exactly was gss said, some horses can't be around others. It's not worth injuring other horses or your own.