Early on, Mearsheimer notes,
The [first?] Clinton administration’s foreign policy rhetoric, for example, was heavily informed by the three main liberal theories of international relations: 1) the claim that prosperous and economically interdependent states are unlikely to fight each other, 2) the claim that democracies do not fight each other, and 3) the claim that international institutions enable states to avoid war and concentrate instead on building cooperative relationships.
The likely or eventual correctness of these three hypotheses are not commented on here. Later, Mearsheimer expounds on the differences between the liberal and the realist schools of international relations thought:
liberals tend to be hopeful about the prospects of making the world safer and more peaceful. Most liberals believe that it is possible to substantially reduce the scourge of war and to increase international prosperity. For this reason, liberal theories are sometimes labelled “utopian” or “idealist.”
He horrifyingly continues, and I’m waiting for the beat to drop because this cannot end well:
Liberalism’s optimistic view of international politics is based on three core beliefs, which are common to almost all of the theories in the paradigm. … [The first and the third are not as terrifying as the second] Second, they emphasize that the internal characteristics of states vary considerably, and that these differences have profound effects on state behavior. Furthermore, liberal theorists often believe that some internal arrangements (e.g., democracy) are inherently preferable to others (e.g., dictatorship). For liberals, therefore, there are “good” and “bad” states in the international system. Good states pursue cooperative policies and hardly ever start wars on their own, whereas bad states cause conflicts with other states and are prone to use force to get their way. Thus, the key to peace is to populate the world with good states.
He concludes his description of the pillars of the liberal view of international politics with
Bad states might be motivated by the desire to gain power at the expense of other states, but that is only because they are misguided. In an ideal world, where there are only good states, power would be largely irrelevant.