In a nutshell, there is a control point that is guarded by an NPC. Once that NPC is disposed of (and there are no other enemies) you can capture the point. It seems simple enough but there are a number of factors unique to each kind of point (resource camp, tower and keep) that I will explain here:
Resource camps are the easiest of the three to take. They have no walls, a few NPCs (five by default, 10 if upgraded), and can be taken easily with a group of five, unless upgraded. You’ll need to take out the Veteran Supervisor NPC to begin the actual capture of the camp.
A group of five can easily take out a resource camp that is lightly defended (one or two players). A second group of five is needed if the camp has been fully upgraded. However, if it is heavily defended, the camp isn’t really worth the manpower, time and effort required as the heavy defenses mean that somewhere out there is another camp completely undefended.
Additionally, if you can’t take the camp, you can still minimize its effectiveness by assassinating the resource caravans that spawn.
Unlike Resource Camps, towers are surrounded by walls and have a single gate which makes them considerably more challenging to capture.
You’ll need about ten players if the tower hasn’t been upgraded, more if it has, and one siege weapon for sure (a flame ram will suffice).
First, take out any oil above the gate. They can really ruin your day. Then build the ram at the gate and knock it down.
Once it’s down most of the attackers should find and eliminate the Tower Lord NPC while some hang back at the entrance to halt reinforcements. Once the NPC is down the actual capture begins. Wait out the progress bar and the point’s yours.
Towers are similar to Resource camps in that if you find a heavily defended tower, it would be a good idea to just move on to one lacking such defenses.
Keeps are an entirely different story compared to towers. Towers are far more common and easier to take than keeps. And since there are only three keeps in the eternal battlegrounds and in the borderlands, it’s very unlikely you’ll come across one that is undefended.
Keeps also have an inner wall that must be broken through, making it twice as difficult to siege. You’ll want to clear any oil from the walls or use catapults to siege the door and mount a defense against reinforcements.
However, if the keep is upgraded enough and has enough defenders, it might be better to pull back and begin building trebuchets. Then start smashing the walls from a distance, forcing the defenders to either force open combat or watch as their walls begin to crumble.
Taking nearby resource camps and stopping enemy caravans is critical to making sure the keep can fall as if the defenders are down on supplies, they cannot repair the walls or build defenses.
Siege weaponry is critical; Arrow Carts are great for taking out choke points and killing personnel, while Flame Rams and Siege Golems are needed to shred down gates.
Catapults and Trebuchets are also needed to take out walls / gates from range. This applies throughout the entire siege. Let’s say you bust into the keep, keeping the enemy from reinforcing is critical, so placing an Arrow Cart at a choke point and having a small team man it is important.
After the outer walls are penetrated another gate / wall needs to come down, and the world needs enough forces to finish off the remaining defenders and take out the keep lord (who is very powerful) before the other world shows up and finishes off a tired and battered force.
For the defenders letting another world beat the outer walls down and moving in after them is a viable and fair tactic. The lesson here is scouting is critical – knowing where the enemy is vital. Smaller groups need to be out in the world communicating on troop movements, denying resources, and tapping control points.
Stonemist Castle is just like a keep, except that it’s an even distance from all three worlds, has a huge wall, and is much harder to siege and defend. Defenders will usually ignore the outer walls, so the true challenge is making it through the inner walls and to the keep lord.