Surprised no one has mentioned a conquest style gamemode like this one:
One team is assigned to defend and one is assigned to attack. The attacking team has to push from their spawn to, lets say, point A and the defending team has to defend it. If the defending team loses the point then they have to retreat to the point behind A, in this case B, and the attacking team has to push again and take point B. Each team would be assigned tickets(for every death they take they lose one) and if a team loses all their tickets they can no longer re-spawn. The only way the defending team can win is if they drain all of the attacking teams tickets, and the only way the attackers can win is if they take all the objectives. The capture zone would consist of a large area, and the attacking team would have to outnumber the defenders in the area to capture it.
It would be something like this. When the attackers take point A the defending team will start spawning near(or inside) point B, while the attackers spawn will move up to point A. Obviously this battle would be on one large map, and the map probably would of had to of been made specifically for the gamemode.