Complex sentence: As a result of the German offensive-Operation "Herbstnebel"-in the Ardennes (also known as the Battle of the Bulge), the Allies had to withdraw resources to stop the German advance in the American First Army's sector.
Split into simpler sentences: As a result of the German offensive-Operation "Herbstnebel"-in the Ardennes (also known as the Battle of the Bulge). The Allies had to withdraw resources to stop the German advance in the American First Army's sector.