Classical Realism vs. Structural Realism

Classical realism as a concept stems from the book The Prince by Niccolo Machiavelli. Classical realists believe that the global system is anarchic, with every state fighting for its survival as it is believed that power is in and of itself the end goal. According to this perspective, states will build military capabilities and implement strong government control to induce fear as a way to gain power and influence, as states must rely on themselves for protection, rather than a third party. Classical realism takes a very pessimistic view on human nature and therefore an unromanticized view towards state interactions. 

Structural realism, also known as neorealism was first outlined in Kenneth Walz’s book Theory of International Politics. Structural realists agree that states are locked in a system of competition for power and survival, however, unlike classical realism, structural realism believes that this is due to the structure of the global political system, rather than human nature. Structural realists do not argue that power is inherently good, but they do believe that it is necessary for survival.

References: 

Leiter, B. (2001). Classical Realism. Philosophical Issues, 11, 244–267. https://www.jstor.org/stable/3050603

Machiavelli, N. (1988). Machiavelli : the prince. (Q. Skinner & R. Price, Eds.). Cambridge University Press.

Waltz, K. N. (1979). Theory of International Politics. McGraw-Hill Humanities, Social Sciences & World Languages.