In world war 1 this was line of fighting that stretched form belgium southward through most of france

The line of fighting that stretched from Belgium southward through most of France in WWI was the Western Front.

Explanation:

The western front was the theater of operations of the First World War that was developed in Luxembourg, Belgium and the northeastern zone of France and opposed, on the one hand, the German empire, with a small subsequent contribution of troops of the Austro-Hungarian empire, and, on the other, France, Belgium, the British Empire, and later Portugal and the United States.

In general, after a rapid advance of the German forces through Belgium and northern France, the French army and the British Expeditionary Corps could contain the offensive in the first battle of the Marne. Then, after the race towards the sea where both sides tried to flank each other, the war lost its mobile character and was fixed in a line of trenches that extended from the North Sea to the Swiss border. This situation remained almost unchanged during 1915, 1916 and 1917, despite massive attacks on both sides and the use of new technologies to try to overcome the situation of blocking, such as chemical warfare, tanks and military aviation. Only in 1918, with new infantry tactics, the war recovered a more fluid character, with the German spring offensive and the subsequent offensive of the one hundred allied days, which definitively ended the war. Despite the almost perennial situation of blockade in the Trench War, this theater of operations was especially decisive and it consumed the most human and material resources to all the powers involved.

the answer is