The game's mission is to defend the galaxy planets from the space invading aliens, you are this Galaxy's last hope, so do your best and defend the paths that lead to your base and to other planets.
There are waves of spaceships rushing towards your base so build many types of towers to defend the well known path. Your success is based on your money, lives and the way you think and build. You start the game with only 150 dollars and for each enemy you destroy you will receive an amount of money. This amount depends on how big the opponent is.
You only have 5 lives and your base wonft handle more than 5 enemies. If the enemy spaceships get through you will lose and you will have to start the level over. Also, try to come up with your attack plan with 2 or 3 waves in advance and manage to earn money so that you are able to improve your towers. You can do this by upgrading the range, fire rate and overall damage. Become the best army space fleet commander out there and beat all the levels Defense:Alien War has to offer.
Good luck and have fun!