Complex sentence: It was the actual seat of power in France, until Louis XIV moved to Versailles in 1682, bringing the government perforce with him; the Louvre remained the formal seat of government to the end of the "Ancien Régime" in 1789.
Split into simpler sentences: It was the actual seat of power in France until Louis XIV moved to Versailles in 1682, bringing the government perforce with him. The Louvre remained the nominal, or formal, seat of government to the end of the "Ancien Régime" in 1789.