Relevant comment quoted in The Economist.
"One thing that I'm taking away from this war is that, in land warfare, the defence remains all-powerful...ground warfare is awful, and it's more awful for the for the attacker...It's more like 1914 or 1861 than 1939 or 1940”—Billy Fabian of @CNASdc.
I'm not sure this is really on topic for EA, but I'll provide a few brief thoughts anyway since I have a sizable amount of adjacent-experience with the topic, since my thesis was on the impact of technological shifts on irregular warfare dynamics.
I can't really get into the question of what WWIII will look like; I'm sure there are plenty of posts out there by people who have spent far more time theorizing about it than I can here.
Thank you for the answer. I thought this might be a topic discussing in the forum, as the shape of future wars seems like a thing that could influence the long term future by a lot.
I don't think that tanks shifted WWI on their own, but more in a combination of changed strategies and tactics. I fear more that a future war would grind to a kind of stalemate quickly, as modern weapons are so lethal (as you described) and favor the defender. Nuclear weapons would be a way to break such a stalemate. Therefore, I fear that this change in war might make the use of nuclear weapons more likely.
A major factor in how future wars play-out is the use of robotics and artificial intelligence. I argued that these factors do tilt toward attrition, as you mentioned, in my essays "Robot War Number One" and "Robot Combat: the Logistics of Ballistics", google-able. The main point is that this attrition will not happen as a static battlefront with masses of people. Instead, it will have depth into foe's heartland, and it will be dispersed. Yet, attrition all the same.
Epistemic Status: Thoughts I came up with after spending too much time on Twitter, so take it with a spoon of salt.
Like many, I was surprised how bad Russia performed in the invasion of Ukraine. One obvious explanation is that Russia just does not have the skills to perform such an operation anymore. While its true that Russia seems to have problems when it comes to things like logistics and morals, I don't think this is the only factor that comes into play. Thanks to support by NATO countries, Ukraine now has a vast amount of next generation anti-tank weapons and they use them with huge success. The Oryx Blog documents losses of equipment in the war and up until now Russia has lost hundreds of their tanks. This seems to be largely due to infantry based anti tank weapons like e.g. Javelin. These kinds of weapons are easy to carry around and show themselves to be capable of destroying even the newest russian tanks like the T-90.
I think this is a possibly substantial shift. The war in Ukraine seems to be showing that tanks are much less effective than they were in the past. Modern war before the arrival of tanks favored the defender extremely. Most notably we can see this in the first world war. While its mainly remembered for its long and bloody stalemate, the first world war had a more mobile component in its beginning. The German made vast gains in the first few weeks of the war. They tried to outflank the Entente, which resulted in a chain of engagements and only ended once they reached the sea and there was no room for maneuvers left. This part of the war was characterized by an extreme loss of life, as artillery and machine guns are extremely deadly if you have no armor to protect you and you have to move anyway. The British Army alone suffered 100.000 casualties in a period of months. After this initial phase, the war shifted to attrition, because no side could overwhelm the defenses of the other.
Shifts in strategy and tactics allowed the Entente to successfully gain the initiative again in the end of the war. One huge component of this were tanks. They broke the stalemate by allowing offensive actions again. Their importance for initiative became even clearer in the second world war in form of the German attack on France. Without the mobility provided by tanks, it would not have been possible.
So, if tanks are much less effective now. Does this mean we will go back to World War I like warfare? Extremely costly mobile warfare, followed by bloody stalemates as no side can overwhelm the other. And if so, what consequences will this have in a world with nuclear weapons? I'd be curious to hear your thoughts here.
There is a paper by two EA researchers (Ben Garfinkel and Allan Dafoe) of some relevance: How does the offense-defense balance scale?