Complex sentence: Rupert was instructed by King Charles to hasten to the relief of York which he relieved on 1 July, but the next day offered battle to the besieging armies and was decisively defeated at the Battle of Marston Moor.
Split into simpler sentences: Rupert was instructed by King Charles to hasten to the relief of York which he relieved on 1 July. The next day, he offered battle to the besieging armies and was decisively defeated at the Battle of Marston Moor.