Nationalism is a political ideology developed in the 18th and 19th centuries that in which the state derives political legitimacy in some way from its population, as opposed to divine right, for example. Nation refers to such a state, its population, and the combinant sociopolitical institution of both government and governed. Since the late 19th century, it has been the dominant paradigm.
Civic nationalism (also civil nationalism) is the form of nationalism in which the state derives political legitimacy from the active participation of its citizenry, the "will of the people"; "political representation". An invididual in such a nation must believe that the state's actions somehow reflect his will, even when specific actions go against his will. Jean-Jacques Rousseau, who first developed this theory, devised the concept of the General Will to explain how that could work. Rousseau put down his theory in various writings, particularly On the Social Contract. See Social contract theories for a more in-depth dicussion of the historical development of this philosophy.
Ethnic nationalism is the form of nationalism in which the state derives political legitimacy from historical cultural or hereditary groupings (ethnicities). This was developed by Johann Gottfried von Herder, who introduced the concept of the Volk (Ger: Folk).
Romantic nationalism (also organic nationalism, identity nationalism) is the form of ethnic nationalism in which the state derives political legitimacy as a natural ("organic") consequence of race; in the spirit of Romanticism and opposed to Enlightenment rationalism. Romantic nationalism relies upon the existence of a historical ethnic culture which meets the Romantic Ideal; folklore developed as a Romantic nationalist concept. The Brothers Grimm were inspired by Herder's writings to create an idealized collection of tales which they labeled as ethnic German. See Populism and Nationalism.
Mazzini (Italy), Michelet (France), Fichte (Germany).
Religious nationalism is the form of nationalism in which the state derives political legitimacy as a consequence of shared religion. Zionism is an example, though many, if not most, forms of ethnic nationalism are in some ways religious nationalism as well. For example, Irish nationalism is associated with Catholicism; Palestinian nationalism is associated with Islam. In general, religious nationalism is viewed as a form of ethnic nationalism.
Sometimes however religion is more of a marker of a group than the motivation for their nationalism. For example although most Irish nationalist leaders of the last 100 years are Catholic, in the 19th Century and expecially in the 18th Century many nationalistic leaders were Protestant. Irish nationalists are not fighting for theological distinctions like transubstanciation, the status of the Virgin Mary, or the primacy of the Pope. Rather they are fighting for an ideology that identifies the geographical island of Ireland with a particular view of Irish culture, which for some nationalists does include Catholicism but has as a more dominant element other elements of culture.
Some political theorists make the case that any discrimination of forms of nationalism is false. All forms of nationalism rely on the population being a nation; that is, that all the members of the population believe that they share some kind of common culture, and culture can't be wholly separated from ethnicity. Even the supposedly ethnically neutral "civic culture" of the United States, for example, relies on English as the one national language, has "God" on its coinage and in its Pledge of Allegiance, and designates official holidays, which promote cultural biases. See also the concept of Manifest Destiny, American nativism, the House Un-American Activities Committee.
The modern vernacular use of nationalism refers to the political (and military) exercise of ethnic and religious nationalism.
In some cases there has been a reaction against nationalism. An example was the perception in pre-World War I European socialist movements that nationalism was being used to prevent workers uniting against capitalism. Another example is in present day Germany and Ireland where there are people who are not comfortable with nationalistic, patriotic, or even cultural symbols that have become associated with violent nationalism.
- Jean-Jacques Rousseau
- Johann Gottfried von Herder, Materials for the Philosophy of the History of Mankind 
Historical events in which nationalism played an essential role included the unification of Italy under the rule of Sardinia and the unification of Germany under the rule of Prussia.
Ethnic nationalist conflicts
(Includes most wars between the 18th century and World War I. Excludes conflicts driven primarily by other ideologies such as religion, communism, or democracy.)
- 1898 -- Spanish-American War
- 1990's -- wars in the former Yugoslavia
- 1990 -- Boxer Rebellion
- 1870-71 -- Franco-Prussian War
- 1914-18 -- World War I
- Middle East
- 1960-2001 -- Basque conflict
Ethnic nationalist organizations
(Not including governments and formal armies)
- Middle East
Nationalism and patriotism
Nationalism and language
A common language has been one of the main presuppositions for nationalism; in France, for example, before the French Revolution patois such as Breton and Occitan were spoken in the various regions which were incomprehensible to each other. Following the Revolution, French was imposed as the national language. For instance, in Brittany Celtic names were forbidden.
German ethnicity in practice during the 19th century was determined as speaking German and having a Germanic name, though with Nazism much more stringent conditions were applied.
Nationalist movements from Ireland to India promote the teaching, preservation, and usage of traditional languages, such as Celtic, Hebrew, and Hindi.
Religious Nationalism and Human Rights, David Little, United States Institute of Peace also discusses history of nationalism, briefly
Internet Modern History Sourcebook: Nationalism there's a lot of information here to incorporate
Alfred Verdross and Othmar Spann: German Romantic Nationalism, National Socialism and International Law, Anthony Carty, European Journal of International Law Google on religious nationalism