it works like this two teams start on opposite sides. there is a space in the center where both teams can meet. there is also a line around that space made by the terrain. at that line there are triggers set up to keep the other team units from crossing the line. If player attempt to force the unit across the unit gets killed. at one hour into the game (about the time when people have large armies) the wonder war will start. you must control the monument and not have any units on the place next to it where the wonder goes for 15 seconds. If you accomplish this then your wonder will appear and now you must defend it.
at no time in the game are people supposed to conquer each other so the triggers prevent you from entering into their bases.
However, there is a bug in the game that effects the scenario. since the triggers on each of the lines are set for each teams player this would be fine. but when the game activates a trigger for a player it activates it for the player that entered into the game in that order. so if you were the first person that entered into the game the game labels you player 1. It doesn't matter if you change to player 6 or any number except 1. When the game activates trigger for player 1 they will effect you. so the first four people that enter the game have to be player numbers 1 through 4. and the same goes for the last four people who enter. otherwise you won't be able to get to the center where all the action is.
I'm currently trying to fix the bug but it may just have to stay that way because it's a game bug.