Imagine modern-day Earth (or the near future) is suddenly involved in a war with an alien civilization (their advancement level is open to change).
Also, for the sake of the argument, assume that cracking the planet is undesirable (the aliens want either resources or territorial expansion).
My main question is how to make sure that the only opposition to the aliens are organized militaries and government agencies, leaving guerrillas, mercenary bands and rebel cells out of the picture. The ideal case is a long, stalemate war (think years at the least) with WW1-style battles.
As I see it, there are a few ways of achieving this:
The Tarkin Doctrine up to eleven
Take the "rule through fear" to its extreme, and take such harsh retaliatory measures against small pockets of resistance that the general population becomes too afraid of resisting. Armies and governments can overcome this by a general "sense of loyalty" or simply because they are too big to be retaliated in this way (for example, the aliens can blow up caves and houses, but not entire cities and fortresses).
If the aliens are advanced enough to bomb a camping site full of rebels they should be capable of bombing an army formation.
Specialized alien military doctrine
The alien troops are somehow immune to guerrilla attacks. For example:
- Their armor/shields are impervious to handguns and small caliber weapons, and only military grade equipment can harm them.
- They carry special riot equipment that makes them extremely efficient against small groups or disorganized soldiers.
- They use some sort of "siege vehicle" good at breaking down improvised barricades, but of limited use against battle tanks and the like.
The earthlings have a special sense of honor
The humans being invaded have a unique perception of honor in combat that forbids them from using "unregulated" or "dishonorable" tactics. As such, they limit themselves to standard, large-scale battles.
If the aliens don't share this trait, the war could potentially be very short, depending on the difference in technology.
The aliens have a special sense of honor
Reversing the situation, in this case it's the invading aliens that have this custom.
In this case, they respect the regular militaries and face them in open combat according to their cultural "rules of engagement". However, rebels and irregular fighters enrage them due to their "lack of civility and honor", and are promptly eradicated to make an example.
This should both remove the current guerrillas as well as preventing more from forming.
Remove the rebels from the equation
A more "out of the box" thinking. The aliens only need control over certain geographical areas, and are content with letting the military patrol cities and try to mount attacks. However, rebels that try to interfere with their controlled areas are abducted or otherwise removed.
This process is easy and cheap enough for the aliens that they don't see the need for more aggressive methods.
One would think that the regular armies would eventually realize the aliens' strategy and try to attack their occupied areas.
Are there other methods that I'm not seeing, or any potential problems with my ideas?