A war is won when both sides see an end to the war as being more favourable than the alternative. As such whilst military gains might drive the decision, the key is a consensus on both sides, that the war should end.
The art of war is building coalitions. The smallest coalition is a group of soldiers who will lay down their lives for each other. The largest coalitions are nations who work together to support one side or other (or merely not to hamper). In this way, even the smallest army can defeat a mighty empire.
The key to winning a war is logistics, for although a battle can be won using the equipment carried to the battle, a war can only be won by feeding men and supplies to the front and regularly rotating men.
Rivers form the frontline in many conflicts, not necessarily because the river is hard to cross, but because a river makes it easy to demarks the territory of one side from the other. As such, because rivers are such obvious features even for the most remote and out of touch general, everyone can agree with the soldiers with their feet in the water, that they are crossing the frontline. Also, rivers naturally flow in valleys, and so from the high ground it is relatively easy to look on the clear ground of the river and see who is crossing.As such, irrespective of the ease of crossing, rivers can become entrenched as a clear barrier separating one side from and as such they can become an uncrossable line.
However frontlines do not exist. They are illusions created by those soldiers who have very little idea what is going on except as far as they can see, and the generals who have no idea what is happening on the ground. A soldier merely knows where they, or their immediate fellows, have been at risk. If they can articulate that risk as “moving from here to there” creates a serious risk of injury or death, that suggests a “barrier” and if that is between them and the known or expected location of enemy forces, then that can be described as a “frontline”. If the enemy also perceives the same increasing risk, then each side may describe areas as “their territory”. Once areas are perceived as “owned” that can increase the risk of moving from “one territory to another” and create an illusion of a “frontline”.
However, the “frontline” is not a single feature. Each section has its own perception of where they “cross into enemy territory”, one that is not necessarily the same as the enemy’s view of when they leave their “own territory”. The combination of each sections “frontline” might be a drawn as a single line on a map, but it is still a combination of different features and not a single feature.
