And now, I'll post a personal experience, since there wasn't time for it last time.
Somewhere south of Meroe
November 17, 319 BC
Gray mist greeted Perdiccas as he rose out of camp and looked into the forest. It had all seemed so easy at first, and now they were fighting an often-unseen enemy. Damn that Alexander for sending him down here!
At first the campaign had gone quite well. Perdiccas' troops had marched to Napata and inflicted a decisive victory against the Kushite army. At Meroe, the capital, the fighting went even better, as the mixed-Macedonian and Egyptian force sacked the city, and capturing the king Nastasen, and captured and killed what a captured Kushite officer was roughly half of their men.
But after that, as the remainder scattered into forest, it had quickly gone south. Karkamani, a fairly high-ranking general, had convinced the scattered Kushite forces that they could not win in open-battle. As Perdicus left Selucus in charge of Meroe's occupation, with a little less than half of the army, and pursued the enemy forces, he started to become quite irritated at the fact that fair amounts of casualties were inflicted on them with small forces, and before more troops could be concentrated to defeat them, they would retreat. Perdiccas spent many long nights agonizing over the lack of a decisive battle.
One day, last October had been the worst. There had been heavy rains, and Perdiccas was unfortunately being led all over the place by Nubian forces. Than they had come under mass attack. The Kushites, hiding in bushes, had attacked them suddenly, inflicting heavy casualties, about a quarter of the army.
Perdiccas got fed up at this point. He had started burning down villages, and killing the people, while leaving small companies to hold down areas he thought were succesfully pacified. But of course, contact had been lost with a number of them particularly in the east.
And yet, Perdiccas was convinced victory would come in another month. The Kushite forces, as far as he could tell, were mostly concentrated in the south-east. Despite the fact that they were recruiting villagers, he thought most of the country would have a hard time attacking in the west, because he had burnt down a good part of the jungle there, and didn't expect anyone from there to attack him. His brain, however always felt like it was going to explode these days.
All of a sudden, from the edge of the camp Kushites started appearing out of nowhere. The mist was slowly clearing and he could tell that about half of them were not dressed in army clothes. And worst yet, they had come from the opposite bank of the river they were camped on. "No this cannot be happening!!" screamed Perdiccas. And then, they were attacked on the forest side by Kushite regulars. But the village people looked way more angry than the regulars. Armed with bows and spears, they had such venom in their look that Perdiccas's heart felt faint. He almost regretted destroying a lot of their country. But the weak feeling was replaced by hot rage, as he saw Kushites dismembering and castrating the corpses of the soldiers, who, being more professional, were starting to counterattack, and were killing about as many of the villagers, as the villagers were of them. And his army still slightly outnumbered them.
"Uncouth barbarians!!" Perdiccas's rage caused him to charge at the villagers himself, armed with his big sword. But about 30 seconds later, a villager who looked more like a monkey than a man impaled a spear through his chest. Perdiccas could feel feet tromping on him for a while, leaving greater pain, then, surprisingly, some of his men were escaping. And then... nothing.