Ultra-nationalism is an overtly strong identification to a society.
"Often, it is the belief that an ethnic group has a right to statehood, or that citizenship in a state should be limited to one ethnic group. It can also include the belief that the state is of primary importance, or the belief that one state is naturally superior to all other states."
Ultra-nationalism is sometimes a response to an event. During World War II when the US fought the Japanese we rounded up US citizens, of Japanese desent, and placed them in internment camps. This can be seen as a form of ultra-nationalism.
Ultra-nationalism is important becasue it can shapes society and governments. It may lead to war, genocide and other atrocities.
Nationalism is the devotion to a person's country and ideals. Ultra-nationalism is this devotion to a greater degree. Now as for how it arises, there is no single cause and easy explanations are not possible. However, if I had to take an educated guess, I would say that it probably starts with a powerful group of people who run a country and start creating an ideology that basically states that they are the best and that other countries are lesser. In time, there will be less cooperation with other nations and thoughts of international interest will be diminished. The problems of ultra-nationalism are great. First of all, it may cause war, if this ultra-nationalism is not checked.
Nationalism is a sense of belonging people have towards their country nation. It inspires feelings such as loyalty to the nation, and pride in its past and present. This feeling of nationalism has become more pronounced in 1700's, That has influenced international relations. The rise of nationalism accompanied the development of concept of nation as a group of people who share a common culture, history, or language and have a feeling of national unity. A nation-state exists when such a group of people occupy an area of land with independent government.
Ultra-nattionalism or extreme nationalism is a form of nationalism in which the loyaly and pride in in ones own people, culture, and history gets converted in to unhealthy sense of superiority in your own type of people and hatered or fear of others. This is the kind of Nationalism that was promoted by people like Hitler and Mussolini.
While nationalism gives people a sense of belonging and pride, and a willingness to make sacrifices for their country. ultra-nationalism creates unhealthy rivalry and tension between nations, promoting desire for for national glory based on domination and exploitation of other nations or people. Extreme nationalism promotes feelings of racial hatred and encourages persecution of minorities.
Extreme nationalism may arise when one group tries to dominate and exploit others to achieve power and prestige for themselves. Ultra-nationalism is often encouraged on the basis of religion accompanied by lack of tolerance for religions other than one's own. Extreme nationalism promotes prejudice by encouraging people to regard people from groups and culture, race, or religion other than yours as inferior. Unfortunately Such prejudice is often passed from generation to generation. Children acquire their prejudiced outlooks from their parents and teachers. These prejudices then also get embedded in institutions, laws, and customs of the society.