Complex sentence: The Gauls demanded that the three should be surrendered to them for violating the law of nations; and when the Roman Senate refused to give up the guilty parties, the Gauls marched against Rome, which they sacked after the battle of the Allia.
Split into simpler sentences: The Gauls demanded that the three should be surrendered to them for violating the law of nations. When the Roman Senate refused to give up the guilty parties, the Gauls marched against Rome, which they sacked after the battle of the Allia.