Orcs

Orcs are savage and brutal. They live in hot plains that are barren and parched but when their populations grow, they venture out and wage wars agains other humanoids and then retreat back to their barren and parched lands with their bounty and slaves. Waging war against them in their homelands would be tough for any other civilization due to the extreme heat and lack of water - thus they feel safe once they retreat back to their homeland.