For the past 200 years or so, nationalism has been an important driving force in political behavior. Nationalism is not universal, not everyone is a nationalist, and it is not always present, but it lies dormant until a threat or opportunity to the nation is perceived by the populace. Nationalism emerged ﬁrst in Europe with the development of the modern state, following the French Revolution. Nationalism has been considered one of the most dangerous sources of political behavior in the 20th century. German nationalism is blamed for World War II, and it certainly played a major role in causing that conﬂict. The nationalisms of various communities in Yugoslavia tore that country apart in the 1990s. Conﬂict between the USA and its Latin American neighbors often rests upon nationalistic indignation by one at the behavior of the other. The causes of nationalism and the impact of nationalism on political behavior are the topics of this chapter. They are illustrated with many examples from diﬀerent regions of the world. Various conﬂict resolution strategies, which can be used to ameliorate these conﬂicts, are then addressed.