Final answer:
Realist and neorealist theories in international relations incorporate human nature, with realism focusing on state security and neorealism on systemic structures; critical theories like Marxism emphasize power dynamics and human ideologies.
Step-by-step explanation:
The theoretical schools of international relations that consider human nature as part of their explanation for the behavior of states in the international system primarily include the realist and neorealist (also known as structural realism) perspectives. Realism focuses on the assumption that states act in a way to secure their own survival within an anarchic international system, often reflecting the nature of the humans who lead them. In contrast, neorealism places greater emphasis on the constraints and opportunities provided by the structure of the international system itself rather than on the individual human nature. However, it also recognizes that the actions and interactions of states are grounded in the dynamics between individual leaders, which are, in turn, rooted in human nature.
Similarly, critical theories, including Marxism, believe that the actions of states are reflected through the ideologies and human nature of those in power, partially explaining state behaviors and systemic injustices within international relations. These perspectives look at the motivations of individual political leaders as well as the broader socioeconomic and political structures that influence state actions.