Catalonia has its own identity, distinct from Spain. The region has its own language, traditions, music, and food, and a long history of struggle against the Spanish state. 
Catalonia’s roots as an independent economic power come from its time as a Greek colony and Roman province. Under the Roman Empire Catalonia became an economically prosperous region with good naval links around the Mediterranean. During the Middle Ages, the Catalans formed their own identity and language. Catalonia was part of the small region of Northern Spain which held out against the encroachment of Muslim invaders. As part of the Crown of Aragon in the later Middle Ages, Catalonia became a powerful maritime empire. Although Spain was eventually united under the rulership of Isabella and Ferdinand, Catalonia would repeatedly come into conflict with the Spanish crown throughout its History. 
Historic Spanish aggression against the Catalans has helped to form their identity as a group, one which has become synonymous with resisting Spanish rule. The official national anthem of Catalonia, the Reapers, was sung during the Catalan revolt against Philip IV of Spain.
Many Catalans point to the war of 1714, when Spain was centralized, as the endpoint of their independence. As with many European groups, the 19th century led to a strong nationalist movement that sought to preserve the region’s identity, language, and customs. Perhaps most important to this sense of identity and dislike of Spanish rule was the repression of the Catalan government and language by General Franco.
Catalonia has a long history as a culturally distinct group. It also has a long history of fighting for its autonomy against Spanish oppression. Many Catalans feel that Catalonia is not Spain, and this should be respected.