How do ideologies shape international relations in general and Middle Eastern countries' relations with the United States in particular? The Clash of Ideologies by Mark L. Haas explores this critical question. Haas's central claim is that leaders' ideological beliefs are likely to have profound effects on these individuals' perceptions of international threats. These threat perceptions, in turn, shape leaders' core security policies, including choices ofallies and enemies and efforts to spread their ideological principles abroad as a key means of advancing their interests.