'pro-nationalistic' is a compound formed from the prefix 'pro-' (from Latin 'pro', meaning 'for' or 'forward') and 'nationalistic' (relating to 'nationalism').

'nationalistic' derives from 'nationalism', which comes from French 'nationalisme' (19th century), from 'national' (from Old French 'nacion'/'national' and Latin 'natio' meaning 'birth' or 'nation'). The prefix 'pro-' has long been used in English to indicate support, so the compound 'pro-nationalistic' developed by combining 'pro-' + 'nationalistic'.

Initially, 'pro-' simply meant 'for' and 'nationalistic' described qualities of 'nationalism'; together they came to mean 'in favor of nationalism' or 'supportive of nationalistic views'.