Henry R. Nau's bestselling book is admired for its even-handed presentation of realism, liberalism, constructivism, and critical theory - and for expertly applying those perspectives in every chapter. It helps students to explore the ways in which these different perspectives shape our understanding of the root causes of historical events and current controversies in world affairs, and learn to think critically. The new Sixth Edition includes updates on Brexit, the rise of Donald Trump and other populist leaders, and continuing developments for ISIS, Syria, and Russia.