Replicants - Fantasy World

Where did the armadas of aliens that pierce the cracks of space without taking into account the costs come from? Why do they persist in searching the vastness of space for planet Earth? For replicants, artificial humans created for war, such questions do not come to mind, because their range of interests is strictly limited. Sometimes, however, fate takes its course, and the one who is made for a few battles or three gets a chance to survive...