The object is to blast through the neutrals in the orange oval before your opponents. From there, you can attack the opposing capitals. This is the only way to defeat your opponents.
You earn bonuses for controlling continents in the large triangle. Each turn you must decide how to allocate your forces between attacking in the ovals, and strenthening your position in the large triangle.
The card bank allows you to earn cards even if you are eliminated from the large triangle.