For millennia there has been a give and take between Offense, and Defense in military technologies. Different technologies being developed changed whether it was easier to defend yourself or to attack others.
When the Persians ran up against Spartan Shield walls they found this asymmetry in cost to be their limiting factor. The Spartans might not have been able to advance, but with their technique and terrain advantage they could defend against the Persians for a much lower cost than the attackers suffered.
This continues to ebb and flow.
A Knights armor kept them safe. Until crossbows made sure it didn’t.
High stone walls kept cities safe from all, but the most determined attackers until Mehmed cracked the walls of Constantinople with his cannons. A new era was born again.
The Naval cannons of Europe allowed them to attack other regions with impunity. Expanding their colonial empires far and wide.
Trench warfare brought the Artillery, and guns of WW1 to heel, and had the war grind to a halt. Paying for every inch in blood.
The Plane in WW2 allowed attacks on enemy positions far behind their lines. Trenches became less effective.
Carrier strike groups, and ICBMs allowed the US to project power globally with little repercussions.
Now though things are changing again. Missile defense systems are getting better. Drone swarms can take down ships with little cost. The most advanced fighter jets are shot down. We are rapidly approaching an Era where defense will once again be easier than offense.
So what does an era like that look like? Well historically Empires borders stabilize. The ones that don’t focus on their internal issues, and were too reliant on constant expansion to prop up their economies collapse in on themselves. Breaking up into smaller regions.
Great power wars also tend to happen in these periods. Not during defensive periods specifically, but during the transition. When one period becomes another. The paradigm shift causes instability, and allows for wars that were previously unthinkable to become reality.
You might think that in a defensive paradigm there are less wars. That’s not the case. It just means that wars when they do happen are costlier for both sides because they last longer.
You can see echoes of this happening. When the US invaded Iraq they used Shock, and Awe, or Blitzkrieg tactics. Quick domination of the enemy. It worked.
They tried to use those same tactics on Iran recently. Iran is still standing. Israel, and the US backed down after realizing their old tactics for a quick victory don’t work anymore.
That doesn’t mean they won’t be back. It just means they’ll have to plan differently. The next time they attack they’ll come prepared for a prolonged conflict.
I think when we are all trying to guess at what will happen next we should keep this ongoing shift in mind. Because it could be a big factor in how the next decade plays out.