Which word best explains nationalism? loyalty ambition confidence gratitude

The best word is "loyalty"

Nationalism is a sense of identity related to the nation you live in, and a related sense of duty and loyalty to that country. Nationalism involves a feeling of connection to your nation, and can include an unquestioning fealty to its leaders. This can be a dangerous thing, as many leaders use nationalism to consolidate power and to justify aggression toward other countries. 

LOYALTY best explains nationalism.