In World War I, which was the line of fighting that stretched from Belgium southward through most of France.?

This was the Western Front. The Western Front is known as being the "main theatre of war" during World War I. This front contained miles of land, including land from Belgium and France. During the war, in 1914, Germany ended up storming the Western Front and tried to take over Belgium, this then allowed them to take over very important parts of France which gave them control. There was lots of new techniques used on the Western Front, including lots of trench war, gases, and military vehicles. Germany could not handle Allied troops which ultimately lead to their downfall.