Complex sentence: It was strategically ineffective, as the Germans indeed invade Belgium, defeated the French army, flanked the Maginot Line, through the Ardennes forest and via the Low countries, completely sweeping by the line and conquering France in days.
Split into simpler sentences: It was strategically ineffective, as the Germans indeed invade Belgium, defeated the French army, flanked the Maginot Line, and proceeded relatively unobstructed. The German army in World War II largely bypassed the Maginot Line by invading through the Ardennes forest and via the Low countries, completely sweeping by the line and conquering France in days.