Hit enter and type "19" (attack), then use the little star button on the control panel and click on the map where to point out where you want them to attack. Sometimes it works ande some times it doesn't seem to. Maybe it depends on what the AI has on it's mind at the moment.
As soon as possible move Alexander and his army and a couple of citizens to the mainland right across from your island, (it's too small to build much of an economy) and ally with the first city state there. This gives you a good base of operations.
If you're having trouble with the pop cap you might be careful about engaging in a very large naval battle, but the city states will be out trying to sink any shipping you have, so you'll need some.
"No good deed goes unpunished."-Murphy