I'm playing 2 vs 2 maps on hard and my allies have been exhibiting strange behavior. The first game my Portuguese allies basically did nothing despite my fending of our opponents attacks, they had plenty of peons but never made a military and as a result were dead almost immediately leaving me hanging and twenty minutes later, dead.
The second game was on the islands map with Spanish allies and after fencing off the shoreline we built massive navies and then invaded....or I invaded while my compatriots left a massive army surrounding their fort for the duration of the game.
The third time with British allies they were aggressive early and on the attack taking the middle section of New England and placing a fort... and that was it. They built a massive army around the fort where it stayed until I crushed the opposition.
I'd say that the game requires you to order them to attack except that they have attacked an opponents cities with small forces in the early ages. What gives?