Complex sentence: Wellington's centre was now on the verge of collapse and wide open to an attack from the French, luckily for Wellington, Pirch I's and Zieten's corps of the Prussian Army were now at hand.
Split into simpler sentences: Wellington's centre was now on the verge of collapse and wide open to an attack from the French. Luckily for Wellington, Pirch I's and Zieten's corps of the Prussian Army were now at hand.