Question: Irish unionists use the two nations theory as a basis for opposing a movement that agitated for self-government that was the dominant political movement of Irish nationalism until when? 
Sentence (from "Pan-Celticism"): Pan-Celticism or Celtic nationalism is a political, social and cultural movement advocating solidarity and cooperation between Celtic nations (both the Gaelic and Brythonic branches) and the modern Celts in North-Western Europe.
Relevant evidence: No