How do the approaches to International Relations (Realism, liberalism, constructivism, etc) inform scholarship on terrorism, guerrillas, international law, ethno-nationalism

Description
How do the approaches to International Relations (Realism, liberalism, constructivism, etc) inform scholarship on terrorism, guerrillas, international law, ethno-nationalism? How do they lay the groundwork and marshal the field of international relations and allow for this more practical, perhaps substantive, content?