How to play Stronghold on Mac

On one of your patrols in deep space you encounter an abandoned base whose self-defense mechanisms are still functional. Upon detecting your presence the base launches several drones to destroy you. After having conquered three of these attack waves a force field containing of three layers will form at the bottom auf the screen protecting a SAM crawler. Your objctive now ist to shoot a gap into the horizontally moving force field in order to eliminate the SAM crawler while still being under attack by hostile drones. As soon as you breached the force field you have to pay attention not being shot down by the SAM crawler which will exploit the fact of you destroying the force field. The game comes with 16 game variations, some of them allowing you to use rapid fire while others make the attack drones invincible for your missiles or produce drones which clone themselves. Still some variants create a force field which will descend from above and is minimzing the space you are able to move in.