Nationalism is the belief in a common culture, or people, and its connection to a particular country. For a deeper discussion of the importance of nationalism(s), see below.
Countries on the Cusp—The Power of Nationalism (by Martha Legace) [1] This will take you to an interview with Harvard Business School Professor Rawi Abdelal where he describes the power nationalism has over new countries—and their far-reaching effects.
Another perspective on nationalism is discussed in the following article by Jerry Z. Muller in Foreign Affairs (March/April 2008), titled Us and Them: The Enduring Power of Ethnic Nationalism. [2]