Guerrilla war is the default.
“We may call this the first system of war. It is the oldest, but as noted above, never entirely goes away. We tend to call this style ‘asymmetric’ or ‘unconventional’ war, but it is the most conventional war – it was the first convention, after all. It is also sometimes denigrated as primitive, but should not be judged so quickly – first system armies have managed to frustrate far stronger opponents when terrain and politics were favorable.”
https://acoup.blog/2021/02/05/collections-the-universal-warrior-part-iia-the-many-faces-of-battle/