Complex sentence: The parties had agreed to a parliamentary process to resolve the issue, but coordinating deliberations between the "cortes" (parliaments) of Aragón, Valencia and Barcelona was made difficult by their diverging interests.
Split into simpler sentences: The parties had agreed to a parliamentary process to resolve the issue. But coordinating deliberations between the "cortes" (parliaments) of Aragón, Valencia and Barcelona was difficult, due to their diverging interests.