I came across a swarm of these red carpenter ants one day. There were probably a couple of dozen of them frantically running around in a small area. I noticed that a few of them were fighting, so I ran and grabbed my camera. It was hard to tell exactly what was going on while I was filming it. When I watched the video on my computer, I was blown away by what I had filmed.
After I started filming, the ants fought like this for at least 30 minutes. I had to leave off a good bit of footage because it was getting too dark, and I lost track of the ants when I ran and grabbed a light and a new camera battery.
All of the ants were attacking a single ant. The ant being attacked is from the same species (camponotus chromaiodes), and presumably from the same colony, so I have no idea why they were attacking him.
The fight got pretty brutal. While I was clipping it together and watching the scenes several times, I noticed a lot of crazy stuff happening which may not be obvious on the first watch. I may come back and annotate the video if enough people are interested.
Best watched on a PC full screen and with max resolution (click the sprocket button at the bottom right of the video, go to quality, and select 720p).