To go a bit more into your overall question (and not into the diagram): No simple “it was because of X” answer will be worth its salt.

One thing that does come close is “better usage of machine guns”. Before WW1 there was still Napoleon style warfare. The French army went in with blue uniforms with red pants instead of anything approaching camouflage, and the Germans with the famous pickelhaube, a helmet with a spike meant to deflect cavalry sabers.

Those armies with those cannons with the wooden wheels, at some point started having smaller cannons that had mechanisms to fire faster, getting closer to what we call a machine gun. But they were still seen as artillery pieces, managed at a higher level, ordered to a more permanent position. Enemy storms your position, if the make it you take the MG back to your second line, pick of those enemies who aren’t dug in yet, and then go back to your first line. You do this with one MG and like, hundreds of guys with bolt action rifles.

In WW2 Germany started out with having an MG per infantry squad of 10 people - and that is still roundabout the ratio of modern armies. Because an MG, set up well somewhere, with just a couple of guys preventing easy flanking, is already a huge problem for any enemy who wants to traverse that area, even if they’re a group of a hundred.

These were incredible strengths; quickly deploying it to make anybody in that direction be in cover or easy pickings, while also quickly REdeploying to make a situation uncomfortable. But it didn’t just take a realization “oh, MG stronk!”, it also took a development of production levels and tactics over years.

But, to segue back into the bigger point of there being no easy answer: All of that is very much connected to your industry. If the Germans would have wanted that ratio at the battle of the Somme, they would have needed roundabout 30000 MGs just for their soldiers who died there!

Then you look at other WW2 developments like the 1-person-carriable mortar. Which can hit people who are in cover, great synergy with an MG - but same thing here, it needs to be produced.

Submachine guns sure make storming a covered position like a trench a lot easier, but 1 of those among your 100 guys won’t make a huge difference against 100 guys defending a trench.

There was a war going on, and A LOT of developments during that war were very much attempts to break that stalemate. Because that would basically be winning.

But there wasn’t that one single trick that did it. It was more that everyone gradually got better and better at fighting it, building up a potential that they kinda couldn’t fully realize because they were exhausted from years of fighting. So when they went into WW2 with that knowledge, but then powered by refreshed industrial capacity, the playing field was just noticably different.

Another perspective that might help understand is to not see trench warfare as a single thing. It got called “trench warfare” because the trenches were a striking feature, but it also consisted of a bunch of other little technologies and tactics. And most things that were developed for this trench warfare war, were still used in WW2. So, this perspective would be more to see it as a gradual change, where that one detail of having trenches at some point dropped out, just like a couple other things did at certain points. The shift from WW1 to WW2 was like shaking a tree so that a bunch of ripe fruit fell out earlier than they would have, had the war gone on.

The biggest game changers towards the end of the war we’re strategic rather than tactical. Namely the economic dominance of the Entente and the crippling blockade of the Central powers. This enabled the Allies to weather the effects of the huge manpower losses in the earlier years of the war.

As far as tactics go, the biggest shift was to move away from the massed infantry assault (big artillery bombardment followed by a massed infantry charge towards the enemy line) and moving more towards infiltration where smaller groups of soldiers would sneak across no man’s land and attack specific installations before the rest of the infantry, now supported by tanks, would attack en masse.

Can’t comment on tactics, but that diagram is not german. Based on the special characters I’d guess something scandinavian.

Combat exercise 3: Break in and fighting in the fortifications interior (24). The goal of this combat exercise is to practice an effective technique to break into enemy firing positions and fight in the interior of the fortifications. This is the teams most demanding task in war. We make a difference between three different targets.

Image captions from L to R:

Targets with individual positions. Targets with built systems of positions. Targets in areas with buildings

SD 3a Take pit* (Breaking into firing position), Crawl & throw and Crawl & Assault Image caption: It is the soldier who is best positioned to throw, that throws the grenades. The division of 1st and 2nd is only made to make explaining the exercise easier. (*trench that is big enough for a couple of soldiers maybe)

Phase 1: Initializing

1st orders: Take pit. Make ready shock/splint (I guess HE/frag grenade). 1st shoots single shots at the enemy position to keep the enemy heads down until the grenades are in the air. 1st evaluates and communicates if possible HIT or MISS for the grenade. Thereafter shifts focus to the depth when the grenade has hit. The procedure is repeated if the first grenade misses. 2nd replies: ACKNOWLEDGED. Announces Shock/Splint and throws hand grenade into the pit.

Phase 2: Assault

After the grenade has exploded the pit is assaulted. 2nd orders: Assault (2nd is the one who threw the grenade). 2nd focuses on the pit. 1st follows 2nd and looks at the area around the target. 1st only shoots when spotting targets. Without hand grenades the task has to be done with (small arms) fire. Suppressing fire then has to be effective until the one who is supposed to take the pit can peep over the edge and can fight (clear the pit) with rapid or automatic fire.

That diagram is probably cryptic to someone who reads German as well, as it is in Norwegian. Not that I have any knowledge to what you’re asking in the first place.

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.