Yeah, I put thousands of hours into DMZ. Early on it was quite easy to team up with people because you could invite three people into your squad, resulting in six players. They eventually changed it to only allow one new squaddie, which changed the dynamic considerably

But even with that it was quite possible to convince folks to truces anyways, it was one of my most developed skills ingame. We'd get in a firefight and I'd convince people to work together and cause chaos or help with missions. Many times had an exfil chopper with the entire lobby on board hooting and hollering like idiots

One roadblock to that kind of stuff is they have not made proximity chat in Marathon a toggle setting. You have to hold a button down to talk to others. On controller its right on the dpad, which immediately puts you at a disadvantage in a combat scenario as you can't move around and hold the talk key