How to get a High Power Rating

I saw that Kraxis only had two cities and decided to take him out.  His lands made an ugly bulge in my border   His first army had Kraxis, 2 heros and 3 Spikes of Kraxis.  After a tough fight I beat and am ready to start the blitzkreig.  However here comes 2 more armies,  all full of militia.  So far I have fought about 10 armies of nothing but militia, with an occasional hero to lead them.  He has apparrently spent the whole game cranking out militia!