Complex sentence: In September the German armies on the Somme lost about the month being the most costly of the battle and combined with losses at Verdun and on the Eastern Front, brought the German empire closer to military collapse than at any time before the autumn of 1918.
Split into simpler sentences: In September the German armies on the Somme lost about the month being the most costly of the battle. Combined with the losses at Verdun and on the Eastern Front, German Empire was brought closer to military collapse than at any time before the autumn of 1918.