What are the similarities and differences between realism and liberalism in International Relations?

In a
sense, approaches to international relations are grounded in assumptions about human nature writ
large. These two different theories are grounded in quite different assumptions about people in
their "natural state." It should be noted that the use of the term "liberal"
in international relations refers to a sense more common in Europe than the United States,
deriving from its Latin root "liber" (free), meaning a position supporting free
markets and limited government regulation.

begins in the work of Thomas
Hobbes, who in his Leviathan famously claimed that the state of nature was
"bellum omnium contra omnes " (war of all against all). Hobbes
assumes that people act entirely out of self-interest and are always competing for resources.
States exist as people band together for safety and security and face off against other states.
Strong, authoritarian states are needed to rein in people's naturally bad tendencies. Rather
than believing that people can work together to attain...