Let's start of then shall we:
Rebels are NOT soldiers. They are rebels.
The taliban countered the soviets with a lot of aid from the US (think of stingers and other goodies).
They also were already skilled in fighting. They were also well adapted to the enviroment, and the soviets were vulnerable. Especially the mountain areas where ideal places for ambushes. The soviets also didn't have that much nightvision and thermal stuff as we have these days. Also, the vehicles of that time where extremely vulnerable to hollow charges and mines/IEDs.
With resources I mean technoligy. Think of thermal vision, night vision, advanced weaponry. They had to fight with what they had, and both the taliban ánd the vietnamese already had lots of experience on their own ground.
An advantage that is above imagination. Knowing how to use the enviroment is a big plus.
With (middle) eastern militaries I mean things like the Iraqi military. Do you still remember how the US rolled over them, because they though digging in tanks and digging trenchlines would work versus hellfires and tungsten / DP uranium rounds?
Also, you want to say that the main fighting force in Vietnam consisted of personel that was already used to Jungle warfare?
That's also why I said "mostly" because there was only a small part of them that knew the Jungle. The Australians in example did a much better job then the US at start. The green berets were only a
fraction of the US forces.
Rebels perform much better then militaries. You know why?
There is no need for long connection lines and incompetent orders. They are mostly based on hit and run actions, based on experience (or that from veterans) and are of an hit and run nature. Simple, but effective. If you know the terrain, making an perfect ambush isn't that hard at all. Small groups are number wise much more effective then groups. Also, the tactics are completely different. Yes, they do take heavy losses, but due to the element of surprise often do a lot of damage.
However, a military has a lot off problems. Making forces move and defend takes a lot of commucations. Most of the time, this is the thing that fails. Also, militaries consist mostly from concripts (the eastern ones) that don't have any experience what so ever. They only have a fraction of the moral that a rebel has. There rebels are fighting for a cause, and soldiers because they have to. If you find yourself greatly outnumbered or outgunned, a soldier will desert much easier then a rebel / freedom fighter. The eastern militaries use old strategies that are outdated, making them effective in an WW2 scenario, but not in modern warfare with guided weapons and nightvision. Big concentrations of forces also allow a easy elimination of them. Trenchlines are outdated. They stopped being effective as an area defence in the 50s. Now, you can only use them as an last ditch defence for things like bases.
And about the Darwin thing. I know that you are religious, and therefore don't accept the Darwin theory. But I'm pretty sure that you know what it is, or else you wouldn't fight it. If you do not know it, it is the survival of the fittest, where Stef related to aswell, earlier on. In this case, the persons that knew how to adapt. Especially in the beginning of the Vietnam war. Rookies got killed alot because they were not familiar with the terrain and the enemy. In the start, guerilla warfare was not very common to the US military yet. Therefore the first ones to enter vietnam didn't know that much of boobytraps, ambushes etc. There were lot of veterans describing walking in an ambush as walking down a forrest path, and then taking heavy fire through a wall of green leaves. Without actually knowing where the shooters were. And about the theory, yes.. this wasn't learned. Thank your God for that, but it was bare reality. The fastest learners make a better chance on the battlefield, always has been, always will be.
Modern militaries therefore use KNOWLEDGE from
all global conflicts and battle situations. Also training their soldiers in things that allies learned or encountered. In "primitive" militaries they use theories as presented in the past, and they don't keep learning.
Nowadays, the US trains their soldiers on all tactics, and not just conventional warfare. This makes improvisation a lot easier when they encounter difficult situations. Whilst primitive militaries are prone to digging in, and making an oldschool trench. "Because that's the way to defend something". Making them all end up dead in an (US) bodybag.
And I still don't know why you have to make this personal. Is this still for the thing we had a few months ago?
I'm not a troll, I'm just posting my, in my eyes well argumented, personal opinion.
I'm just saying that THEORY and technological supremacy are vital on the modern day battlefield.
For example, we are much more effective in avoiding IEDs, avoiding ambushes and fighting the "invisible enemy" etc due to the things we learned from the soviets. We don't only learn from our own mistakes, but also from the mistakes from others. Also, the large amount of modern technology (especially nightvision and thermals) adds a lot to our supremacy these days. That is why we should keep investing in military technology and training, and I'm pretty sure that you agree to that, or else you wouldn't have posted this.
They should only avoid learning to much about one conflict, for example afghanistan on the moment. They should learn a lot more. There is a lot of useless time spending in the military. This should be filled up with training. Maybe even with realistic training with for example realistic paintball or laser weapons. And yes, there is not that much money available. Well, I'd skip a lot of stuff from the political agenda, and invest more in the military. I'd also not invade that many countries, because it costs a lot of lifes and money. And I'd rather have a smaller military then an extremely large one. I think the US would still be powerful enough if they only had 70% of their forces. Instead of spending training and equipment/materials (buildings, vehicles, supplies etc) in the other 30%, I'd invest the same amount of money in the other 70% (or even more) to give them a larger advantage.
Think of the armors from modern fighting vehicles. While the europeans have somesort of ceramic "sponge" to counter hollow charges (like RPGs). It consists of an main armor, with spaced second and third armor, filled with a brittle ceramic lightweight bubbly filler that absorbs most of the power from an RPG. For example, look at the German PUMA ifv, that went in mass production earlier this year. the US uses their initial solution, the "cage".

It works..... kind off.
They still use outdated M2 bradleys (fielded in the early 80s). Yes, they do "update" them, but that doesn't really do the job that well. Why? Well, it's cheaper. While just about all European nations work on (combined) projects to protect their soldiers better, and making them more effective. They are planning to replace the Bradley in 2018 (!), with the GCV ifv.
The US has a lot off future projects indeed, but they are still far from where they should be right now. That really has to change in the future. That is why I thought all attemps to it are to be higly encouraged.
http://en.wikipedia.org/wiki/Puma_(IFV)
Here's some more info on the Puma. And yes, I also do know that you hate wiki pages as a source, but this is accurate information on the Puma.
Also think about the main infantry rifles. The M16/M4. They have better options readilly available (the HK416 thats almost a M16, the G36 (based on the AR18), and numerous improved M16 systems from the US themselves. Allowing for better accuracy and even more important, reliability. Focussing on technology should be a priority, like Germany. They are doing the right job at the moment.