Who is Stronger?

A tower defense game set in near-future East Asia (plus USA): Aliens are attacking the countries of the players - they appear on the top of the board and are pushed down, when more aliens appear. Aliens that reach the bottom destroy the buildings there. Players can fight the aliens by buying military units - They destroy the aliens, which then leave a "core" that can be exchanged for money. Your objective depends partly on your secret objective card - some gain points for helping the aliens destroy certain opponents, others have to concentrate on defense or making money. There is only one winner. —user summary