Complex sentence: 'Máel Coluim (II) mac Cináeda (Malcolm son of Cyneth, king of Scots) and Owain the Bald (King of Strathclyde) defeated Earl Uhtred's forces determining the eastern border of Scotland at the River Tweed.
Split into simpler sentences: 'Máel Coluim (II) mac Cináeda (Malcolm son of Cyneth, king of Scots) and Owain the Bald (King of Strathclyde). Their combined forces defeated Earl Uhtred's forces determining the eastern border of Scotland at the River Tweed.