Complex sentence: Amherst fought with the Hessians at the Battle of Hastenbeck in July 1757: the Allied defeat there forced the army into a steady retreat northwards to Stade on the North Sea coast.
Split into simpler sentences: Amherst fought with the Hessians at the Battle of Hastenbeck in July 1757. The Allied defeat there forced the army into a steady retreat northwards to Stade on the North Sea coast.