On the battlefield you have 2 methods of attack/strategy. You can deploy units you built on your base, you can also use command powers you unlock and upgrade in the research building.
Your command powers (a-10 strike, orbital cannon, etc) cost command points each match. You earn command points by destroying buildings on base. If you ran out, you will see them replenish as you take out more buildings.
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Empires & Allies Game GUIDE