You're wrong. People play like being in a war against an enemy army. You the commander are the general, but the people on the lines are the heroes. They decide what happens, you decide the path you want to take based on the ability of the troops you command, and the best strategy for the terrain (map). They make it happen, or not. If Empires worked properly, commanders would be able to adapt their tactics according to how the battlefield evolves, and create complex strategies that players can try. The reason you can't do such complex strategies in many regular rts's is precisely because the units do not have a functioning brain. They can't make tactical decisions on the fly and adapt their playstyle to ensure the success of their mission. RTS units also can't deny their orders in favour of another objective that is more apparent on the ground. This is where commanding comes in - if you're a good commander, the troops will trust your decisions and go for your objectives rather than their own. If you are not, or if the player is rogue, then they will freelance at whatever they want. The lack of controls on players means it really is up to the leadership skill of the commander to get players to work together. There doesn't really need to be an incentive, because if you trust your commander, the incentive is that you defeat the enemy, and by doing so, win.