The national feelings of people in their certain country has always been present in all over the world. It sometimes is carried to extremes resulting in chauvinism.Then it changes the whole history of that particular nation, and sometimes even the whole world.
First of all what is really behind the word "nationalism". The dictionary defines it as;
"Patriotic feelings, principles, or efforts."
So it is actually not a bad thing. It helps bringing forth economic growth and public wealth and wellness.
There has been plenty of example of nationalism. One prime example of a person with strong national feelings were István Széchényi who, seeing how underdeveloped his beloved Hungary was in the early 1800s compared to the West, but especially to Austria, he started reforms that he did not benefit from. For example, when the National Diet was debating whether a national, where the subjects were thought in Hungarian, university should be founded or not. As a sign of his patriotic feelings, he offered a whole year's income of his, (70,000 Forints at that time).
Nationalism, as I have mentioned before, sometimes are taken to extremes. Chauvinism, when the patriotic feelings become too intense and extreme, lots of wars and violence conflicts. We don't have to go very far back in time to be able to find an example of it. The Kosovar conflict is a really good example of chauvinism
Kosovo was a part of Jugoslavia. The majority ethnic group there is the Albanian. The whole conflict started out by the Kosovars forming an army, terrorizing, and demanding territorrial autonomy. So the Jugoslavians, including Milosevics, started doing ethnic cleansing on the Kosovar Albanians. So the NATO started bombing Jugoslavia which made Jugoslavians hate NATO, especially the United States, causing the rise of nationalism and chauvinism among the Serbs.
I, personally, think that, chauvinism, or nationalism is probably always a good and positive feeling.Chauvinism is not allways good.