Ask Lemmy

Not really a WWI expert, but I believe that you are correct that the big factor was Germany running out of manpower.

There were also technological advances, like the rolling barrage that moved immediately in front of an advance to suppress defenders. Or the early tank. But I don't think that these fundamentally changed the situation. They alome wouldn't have broken a static situation.

searches

Wikipedia apparently calls it a "creeping barrage":

https://en.wikipedia.org/wiki/Barrage_(artillery)

A report said "Experience has shown that it is far better to risk a few casualties from an occasional short round from our own artillery than to suffer the many casualties which occur when the bombardment is not closely followed up".[21] A creeping barrage was essential to the success of the Canadian Expeditionary Force in the capture of Vimy Ridge in April, 1917. The creeping barrage was used during the action of Tell 'Asur on 12 March 1918 in the Sinai and Palestine Campaign.[22] Six months later, it was used with devastating effect during the Battle of Megiddo (1918) when 18-pdr and Royal Horse Artillery formed a creeping barrage which fired in front of the advancing infantry up to their extreme range while 4.5-inch howitzers fired beyond the barrage, while heavy artillery were employed in counter battery work.[23] The creeping barrage moved at a rate of between 50 yards (46 m), 75 yards (69 m) and 100 yards (91 m) per minute.[24]

https://en.wikipedia.org/wiki/Tanks_in_World_War_I

The development of tanks in World War I was a response to the stalemate that developed on the Western Front. Although vehicles that incorporated the basic principles of the tank (armour, firepower, and all-terrain mobility) had been projected in the decade or so before the War, it was the alarmingly heavy casualties of the start of its trench warfare that stimulated development.[1][2] Research took place in both Great Britain and France, with Germany only belatedly following the Allies' lead.

Fuller's Plan 1919, involving massive use of tanks for an offensive, was never used because the blockade of Germany and the entry of the US brought an end to the war.

I think that someone could argue that tanks were becoming a more important factor in late WWI facilitating the offensive, but they weren't yet a major factor.

You could argue that air power, which was also emerging, would help the offensive, but that was even further out from becoming a major factor.

I think that it's fair to say that the machine gun, barbed wire, and the trench (maybe also the land mine, though I don't recall seeing that normally listed with the above three) favored the defensive, and that over time, other factors would come to the fore that would favor the offensive. You could say that those factors were becoming more prominent in late WWI. I don't think that one could say that those were the dominant factors in ending the war, though.

That is to say, the only defense against the new weaponry was to dig trenches, and the only way to capture trenches was to throw a few thousand men at them, at which point, you may have gained a few hundred yards.

The thing about trench warfare that makes it potent as a defensive measure isn't the idea that no trenches can ever be captured. It's that it slows and limits any offensive to the point that the other side cannot perform a "breakthrough", to both penetrate enemy lines and then be able to greatly exploit that situation. https://en.wikipedia.org/wiki/Breakthrough_(military)

A breakthrough occurs when an offensive force has broken or penetrated an opponent's defensive line, and rapidly exploits the gap.[1]

Usually, large force is employed on a relatively small portion of the front to achieve this. While the line may have held for a long while prior to the breakthrough, the breakthrough happens suddenly when the pressure on the defender causes him to "snap".

As the first defensive unit breaks, the adjacent units suffer adverse results from this (spreading panic, additional defensive angles, threat to supply lines). Since they were already pressured, this leads them to "snap" as well, causing a domino-like collapse of the defensive system. The defensive force thus evaporates at the breakthrough point, letting the attacker to rapidly move troops into the gap, exploiting the breakthrough in width (by attacking enemy units at the edge of the breakthrough, so widening it), in depth (advancing into enemy territory towards strategic objectives), or a combination of both.

Germany achieved a breakthrough against French forces in WWII---they penetrated French lines and were able to, from that point, conduct a sustained offensive that led to major gains, wirh France unable to stabilize the front.

That's the kind of thing you'd need to be able to consistently do against trench fortifications for the trenches not to be useful. If a defender can slow an advance enough that they can just dig more trenches or limit an attackers gains to a small amount and then quickly counterattack and retake them, the trenches retain their value.

that credits light machine gun units (with ample supplies of grenades) for breaking the stalemate.

I think that that tactic of having more firepower from light machine guns was tried. I don't think that it could be said to have defeated the use of trench fortifications.

https://en.wikipedia.org/wiki/Marching_fire

Marching fire, also known as walking fire, is a military tactic—a form of suppressive fire used during an infantry assault or combined arms assault. Advancing units fire their weapons without stopping to aim, in an attempt to pin down enemy defenders. Marching fire usually ends with an infantry charge to engage the enemy in close combat. The tactic requires ample ammunition and rapid-fire weapons.

The modern form of marching fire evolved in the early 20th century from a French Army infantry assault concept which suggested the use of suppressive fire from a light machine gun carried by one man—the Chauchat automatic rifle. The tactic was employed to a limited degree in World War I then further codified with the introduction of the M1918 Browning Automatic Rifle and described in U.S. small unit infantry tactics manuals in the early 1920s.

In 1903, French military theorists noticed that the machine guns of the day, heavy and relatively immobile, were of little use in infantry assaults. They determined that "the machine gun must learn to walk".[3] A marching fire tactic (French: feu de marche) was expected to involve incidental suppressive fire, with the advancing troops considered a deadlier threat than the unaimed bullets, causing the enemy to fall back.