Mearsheimer explains the fundamental division within realism by defining two sections of political realism: Human-Nature Realism and Structural Realism. The names of the two types of realism are very self-explanatory in terms of explaining the division: HN Realism argues that states are constantly vying to increase their own power and peace is non-perpetual because our human nature is selfish, power-hungry and innately aggressive (ie. HN Realism can be derived from Thomas Hobbes’ theory on the State of Nature and Morgenthau’s theory of Animus Dominandi [explained in paragraph three]). While HN Realism believes that it is the state’s innate nature to act that way, Structural Realism argues that it is the structure of the International System that explains how states behave: states live in an anarchic system and can never be sure whether their neighbouring states will be non-aggressive in their foreign affairs. This is why a state has to increase their power to become as powerful as possible (example of the USA as a hegemon in the West) so that their security can never be threatened by neighbouring nations.
He explains that the most ideal situation is to be so powerful that no other nation can ever threaten your security. This essentially means that a nation cannot be small and weak because they are vulnerable, so states have to try their best to maximise their power. The most ideal situation, therefore, is being a hegemon: a regional superpower that is clearly the strongest economically, politically and militarily. Power ensures that no other state has the capacity to cause harm for your state and this is exactly what is going on in the USA: they are a hegemon in the West so they never have to fret that Canada or Mexico (their neighbours) will launch an attack on them.
Animus Dominandi is a term often used in Morgenthau’s description of Human-Nature Realism. Morgenthau’s take on realism is that human beings are hardwired with animus dominandi so we are all born with Type-A personalities meaning that we pursue power as an end [this is our HUMAN NATURE]. Because everyone is power-hungry, this projects itself onto a state’s foreign affairs, resulting in states acting in a realist fashion.
As it has been established that the most ideal situation for a state is to be a hegemon, every nation is constantly trying to increase their power (be it through economic growth, military expenditure or increased involvement in the UN). Power acts as a mean of deterrence so Mearsheimer predicts that, if we are indeed living in a Realist world, China will attempt to become a Hegemon in the East by turning their economic power into military power. China was always considered an underdog in the East (overshadowed by the USSR, Japan and other powerful nations) but after the Korean War of the 1950s, they emerged a powerful nation whose power was constantly evolving. China has become increasingly aggressive in their power play (eg. by trying to fight for the occupation of the South China Sea) and this is why Mearsheimer is certain that China will try to increase their power ten-fold. But this will have ripple effects that will have negative implications on China: the USA will not want China to dominate the East and neither will other nations in the East. Therefore, the USA will go to great extents to prevent their rise of power and work towards cooperating with Asian nations to instil containment policies (similar to the containment of communism during the Cold War). This will lead to a very large security competition and Mearsheimer fears there will be repercussions as he stated that “China will not rise peacefully.”