In order to make your enemies as your allies just follow this. First, build a very vast 
military base. Don't concentrate on creating extra villagers. If you are playing a random
map with more than two enemies then one of them will be concentrating to build a forward 
military base like you and the other will be concentrating in creating extra villagers to
build temples, markets and Wonder. This you could easily see from the mini-map. Now bring
your large army to the enemy base that concentrates on creating villagers, destroy their 
wonder and temples. The enemy at once gets stunned to see your ambush attack and they will
change their diplomatic stance to ally. Atonce you should set your diplomacy to ally if 
you are too late then they will again set their stance to enemy. Try it, It really happens.
This technique is common to both Age of Empires-I and Age of Empires-Rise of Rome. If more 
doubts persists, Mail me.