Complex sentence: In 1138, Robert declared his support for the Empress Matilda, but he was defeated in Normandy by Waleran and his English allies were crushed by Stephen and driven back on his fortress of Bristol.
Split into simpler sentences: In 1138, Robert declared his support for the Empress Matilda. Unfortunately he was defeated in Normandy by Waleran and his English allies were crushed by Stephen and driven back on his fortress of Bristol.