Which of realism, liberalism, and constructivism best characterizes the relationship among nations?
I tend to believe most in constructivism as I do not believe that either realism or liberalism takes into account the attitudes of nations towards one another.
Realists argue that all nations act only to get more power or to maintain the power that they have. According to this theory, international relations are Hobbesian -- a war of each against all. But this makes no sense. For example, if this is true, the US should fear British nuclear weapons just as much as Iranian ones. That does not make sense.
Liberals argue that democracy and international interactions will lead to peace. This seems too simplistic. The US and China interact in many ways all the time. Even so, there are still tensions between the two.
By contrast, constructivism is much more nuanced. It argues that nations conduct themselves based on how they perceive themselves and others. This makes more sense to me. It tells us, for example, that the US and Britain do not fear one another because they have a long history of friendship and many ties of culture. Neither realism nor idealism takes this sort of friendship into account.