That's might sound a bit off topic but... ALL modern "wars" so far (in quotes because modern wars seen the past ones are veeeery asymmetrical) have proven a thing: tech makes difference to a certain extent, but in the end motivated boots on ground decide, the classic western doctrine "few and well armed" have failed the real life test.

That's means: we can perhaps made super-duper powerful fighter jets able to hit any target on earth unseen by no one, unstoppable. That's can just destroy the enemy army/infra, if that's the real target ok. BUT if the target is a bit more than just crushing enemy infrastructures/army (perhaps because the war have the exact purpose to grab those infra/resources that need them) the result of such hi-tech war is a sea of destruction, big amount of resources and life lost, people starving to the destruction but no winner.

I'm convinced that more than hi tech combat systems we need many low tech, low costs weaponry + deterrence capacity (nukes). An enemy of course can hit some of them, some part of domestic infra easily with his super-hi-tech systems but can't really win. No one can produce enough of EuroFighters, F35, Su35, FCAS, DDG-X etc to really crash a swarm of simple and cheap war machines dispersed on the ground. Soviet Union discover that in Afghanistan, USA repeat the same mistake already made in Vietnam in the same country, France idem in Libya and Mali etc and in all those cases the enemy was just armed with limited tech against hi tech weaponry, logistic, TLCs etc.

It's not much different than the classic mainframe vs cluster. Modern hyper-expensive systems are powerful SPOF while a cluster can survive on far less nodes. Similarly a country with a distributed enough productive and civil infrastructure can't easily be hit. An enemy can hit a target, few targets, but keep doing so with very expensive and so not much numerous weaponry means just having created destruction so entering the country still demand boots on ground, and on destroyed infra with a now very angry population that have nothing more to loose it's hard and nightmarish, beside that having wiped out most valuable infra at high prices (hi tech is costly) there is the need to rebuild many things because no war typically have the sole purpose of destruction, except those suicidal. Try to sell themselves to the defeated enemy to "morally" conquer it, as per Clausewitz classic, also fail the defeated survivors are not just "people who want the peace again", they have lost anything and they are very angry, some, probably the most wealthy and the most poor might change flag quickly the big mass of all other will not.

In defensive terms that's not much better, the better defense is the attack capacity, witch means nukes these days, not few big but many small that can be smuggled in/around the enemy territory to give back a so deep wave of destruction no one is really interested to attack you first. The rest is these days not "classic war", like propaganda, corruptions, sabotage, etc.

Long story short: to protect themselves nations should look at classic Swiss, Sweden, a small professional army for the few big weapons, all able population trained and armed at home, regular yearly based not-that-long and well paid exercise etc. To conquer there is a big need of powerful propaganda (we have it, too much and in wrong hands these days) to motivate people to go to war and than a guerrilla like invasion after classic asymmetric war techniques to weaken the enemy, in any case a war preps can't be hidden these days so attacks by surprise are a thing just on very local scale.