Before WWI, strategically, machine guns were offensive weapons. They were used to expand the European empires against opponents who didn’t have them.
Come WWI, it turned out that they were defensive weapons which made offensive operations very hard if both sides had them.
Armor and air made fast offensive operations possible in WWII, and aircraft carriers made air the queen of the ocean and the king of force projection against nations without large air forces.
Over the past twenty years two major things have changed in military technology. I’ve written about both in the past.
The first is the spread of cheap and effective drones and missiles. It was always clear that drones were not going to be weapons of the powerful. What matters for weapons systems is who can afford them. If you need aircraft carriers and you’re not a major country, you’re shit outta luck. The end of medieval nobility arrived with gunpowder weapons, specifically cannons. King could afford them, nobles couldn’t, and old style castles couldn’t stand against them.
Another thing about drones and missiles right now is that defenses against them aren’t very good. Hit missile defenses with a large enough wave of attack and some will get thru, and if you have decent intelligence, some will get thru and destroy some of the air defenses.
In the old days if you wanted to bomb, bomb away and inflict terrific damage on someone without them being able to strike back, you had to have a lot of aircraft and either basing rights or aircraft carriers. Now they just have to be in missile and drone range. And often the missiles and drones are way cheaper than the defenses.
This means it’s easy to hurt the other guy. No more Israel pounding Lebanon and Lebanon can’t strike back, even though Israel’s military budget is way more than Hezbollah’s. Likewise missiles and drones are great at shutting down naval traffic, as the US, UK and Israel are discovering.
But what has happened at the same time is increased strategic ability to defend. Improvised explosive devices, cheap drones and missiles, and the way that armor (tanks, etc…) has become almost worthless. You can’t punch thru, anymore, if you don’t exhaust the defender first or take them by surprise. We’ve seen that in Afghanistan, but we saw lesser version in Iraq and Afghanistan; the US could take the cities, but everywhere else they were in danger: take out a convoy and get hit by IEDs and guerilla attacks.
It’s easy to hurt the other guy, but it’s very had to take and keep territory. “Big Arrow” war requires massive overmatch in forces.
To put it crudely, any pint-sized country or reasonable sized militia is in the game: they have weapons that can threaten anyone near them. There’s no “stand off and bomb”, not even for the US, unless it wants to withdraw from its overseas bases. The enemy can almost always hit back. If Israel goes to war with Hezbollah, Hezbollah, with at least 150k missiles can and will flatten Tel Aviv if Israel decides to flatten Beiruit.
One-sided deterrence is broken. “You win on the ground quickly and you can’t hit us from the air without us being able to retaliate.”
That the new military technology status quo. There are exceptions, and there are particular cases (many people think that navies are essentially obsolete except for submarines in any real war, and submarine detection technology is advancing so quickly that even subs may be useless soon.) But basically, it’s hard to conquer someone who’s properly prepared (Armenia was not, Ukraine was, Hezbollah is, Hamas is.) And it’s hard to shut down drone and missile based retaliation, so you can’t have nice little colonial wars like Gulf I where you hit them and hit them and all they can do is take it.
War, war always changes.