For hundreds of years realists have debated idealists about the nature of the interstate system and the most effective means to promote the endurance of the system and the survival of individual states. This paper uses a computer simulation called EARTH (Exploring Alternative Realpolitik Theses) to explore the viability of collective security in a realist world. The results of our experiments indicate that the practice of collective security promotes the endurance of the entire system. Our results also show that states that practice collective security principles are more likely to survive in a realist world than states that operate according to realist principles