Complex sentence: On 8 July Joffre decided to attack in Champagne, with a supporting attack in Artois a few days earlier to attract German reserves and accepted claims by Castelnau that up to of ground could be gained in twenty-four hours.
Split into simpler sentences: On 8 July, Joffre decided to attack in Champagne, with a supporting attack in Artois a few days earlier, to attract German reserves. Joffre had accepted claims by Castelnau, that up to of ground could be gained in twenty-four hours.