What's this movie ? I don't remember the name but I remember what it's about.?

I think it was like some futuristic warzone where there was these band of rebel people who killed the 'normal' people, I remember some police-type people who were there trying to find out about the situation. I remember the main leader of the rebels had blonde mohawk and he also had a girlfriend who had her head chopped off through the movie, near the end bit I remember him chasing them in a car with a bunch of his rebel friends behind him. I also remember they went through a drainage system to get back to where they were going (unless that was a different movie) also the brother of the rebel leader was also a king of somthing on another side ? was years ago that I watched this but I remember I liked it and would like to watch it again.