You have no idea what a massive gulf in technology between modern weapons and the weapons, in the conflicts you are talking about, is!
While in American Revolution and Vietnam war one side had a considerable advantage with better weapons, tactics. The other side would be able to counter that with their own tactics, manpower and pose a considerable threat to the side that's technologically more advanced.
With modern technology the gulf is enormous.
You can hit a modern tank with it's reactive armor with rocket launchers from 90's. But it will keep on going even with couple of dozen hits. And it will counter attacking forces with suppression fire while networking your exact location to extremely accurate artillery support units, aircraft with precision weapons and support infantry with mortars and so on.
You can send 5 state of the art tanks from 1990's/2,000's and 2 of them will be exploding in fireballs, before they even realize they are in the battle zone. Other 3 will be under artillery fire/air attack.
The aircraft from 2000's with 20 year old electronics will be shot down without ever being able to lock on the enemy aircraft. And if by some chance it does manage to fire of a rocket, it will most likely be defeated by enemy aircraft electronic warfare systems and countermeasures.
Your older Surface to air missile unit will have to fire semi-blind as it can only switch radars for a few seconds to get a lock. Then switch off and hope there isn't a rocket already flying towards it. From deadly anti-radar electronic warfare systems. Even if you remove all the electronic warfare jamming that will make much of your equipment behave in malfunctioning manner: Your SAM missiles without radar guidance will have extremely hard time maintaining lock on target vs electronic warfare jamming, counter measures from enemy aircraft itself.
Your semi-accurate Artillery, shooting on enemy infantry, will be quickly pinpointed by electronic detection systems. And you'll have bunch of extremely accurate thermobaric rounds coming your way. Putting oxygen around you on fire. Unless you get hit by a precision 2,000 pound bomb coming to you from the sky.
The enemy will force you to engage them and concentrate your forces then hit you with extremely accurate artillery and air support. Your thousand man strong unit will perish in mere minutes.
All you can do is abandon your heavy equipment and hide in caves, forests and cities. In small groups, taking potshots at enemy.
100,000 people with rifles and old infantry weapons are just a nuisance for units equipped with modern warfare systems.
You really have to look at Iraq, NATO bombing of Yugoslavia, etc. To get a picture of how ineffective 20 year old equipment is against more modern weapons in today's warfare environment.
