Complex sentence: A state's power in international politics, Mearsheimer argues, derives from the strength of its military for two reasons because land force is the dominant military power in the modern era, and because large bodies of water limit the power projection capabilities of land armies.
Split into simpler sentences: A state's power in international politics, Mearsheimer argues, derives from the strength of its military for two reasons. First, because land force is the dominant military power in the modern era, and second, because large bodies of water limit the power projection capabilities of land armies.