Heres an easy way of beating a computer enemy using Usa. First make your starting dozer build a fusion reactor.Then go to your center of commandiness and build 6 dozers. once the first dozer is ready build a barracks.By that time your reactor should nearly be finished.When it is build another one and then another dozer will be built.Use it to make a supply centre. use any other ones to build any defences you need.after youve built your supply build 3 war factories or 5 air fields and build loads of tanks/planes.it doesnt take long.after you think you have enough attack.this is even more easy if you do it as fast as you can.