This bonus makes your enemy's vehicles spawn heavily damaged. When you conquer all the planets on the map, you must defeat the enemy in their base planet in order to have conquered the galaxy. Every four victories, you are also allowed to use a bonus that either automatically gains you the planet or destroys the planet. Each planet, when conquered, has a special bonus that can help you.
Galactic Conquest is a special mode that lets you choose a faction and lead it to victory by conquering all of the planets on a map.