Nationalism is an idea and movement that holds that the nation should be congruent with the state. As a movement, nationalism tends to promote the interests of a particular nation (as in a group of people), especially with the aim of gaining and maintaining the nation's sovereignty (self-governance) over its homeland.
Nationalism is the belief that your own country is better than all others. Sometimes nationalism makes people not want to work with other countries to solve shared problems. Patriotism is a healthy pride in your country that brings about feelings of loyalty and a desire to help other citizens.