What are the differences between the “theories” (realism, liberalism and Marxism) vs the “approaches” (rational choice and constructivism) in international law?

1.What are the differences between the “theories” (realism, liberalism and Marxism) vs the “approaches” (rational choice and constructivism) in international law? Is this distinction useful? Why or why not?2.Which of the three theories (liberalism, realism, and Marxism) is most optimistic about international law? Which is most pessimistic and why?