[@Aqutanama]

So the way this world works is that there are about five great land masses or continents. Each continent is ruled by a militaristic regime. About 30 percent of each continent is comprised of urban, suburban, and rural areas that are well protected behind walls and defence systems. The other 70 percent of the world's land mass is an open battlefield. 

There are some rouge civilizations that live out in the 70 percent war zone, but they are small and well hidden and/or well defended. 

The only type of weapon that is forbidden are nuclear weapons, but everyone has them in abundance. Basically, mutually assured destruction is the main motivating factor in not using nukes. Poison gasses aren't a huge threat, as almost any helmet will have top notch filtration and self sufficient air supply. Also, since they've been at war for so long, their bodies have grown resistant to poison and almost any kind of sickness. 

They eat like we do. They raise farm animals that are basically like our own here on Earth, but they are generally larger, through genetic engineering. Same goes for fruits and vegetables. They might not have as much area to farm, but they have found ways to maximize output. Also, the world's population is only 1 billion people, because war keeps the population count down. 

There aren't any rules against harming civilians, but it is impractical. Even the most important civilian, if held hostage would be left behind by their government. Everyone on this planet knows that you could die at any time, so they don't fret if even their warlord/president is killed. They just raise the next in line to take the spot. Also, the cities and protected areas are so well protected, it's impractical to attack a city (though there are no officially off limits zones).

The main way war is fought is by attacking supply routes of your enemy. Each continent has to transport raw materials from one protected zone to the other. Like transporting food or metal ores from well protected rural areas and mines to the cities. That is when you are most vulnerable. So basically, all nations have a half of their armies on home soil, protecting their shipments. And half of their army is out attacking their enemies' shipments. Then or course, there are the battles fought to keep your enemy off your continent in the first place. 

Alliances have been made in the past, but currently, it is every continent for itself. 

Any more questions? I like answering them.