Let's talk about guerrilla warfare.
When did it start?
When and where did it consolidate into a coherent doctrine?
How is it related to other military developments like conscription, and to political developments like nationalism and democracy?
What doctrine has proven to be effective in quelling it? Has there even been one?
>The Fabian strategy is a military strategy where pitched battles and frontal assaults are avoided in favor of wearing down an opponent through a war of attrition and indirection. While avoiding decisive battles, the side employing this strategy harasses its enemy through skirmishes to cause attrition, disrupt supply and affect morale. Employment of this strategy implies that the side adopting this strategy believes time is on its side, but it may also be adopted when no feasible alternative strategy can be devised.
>When did it start?
Probably in prehistory.
>When and where did it consolidate into a coherent doctrine?
I would argue it still hasn't. You have a variance of different doctrines, which share some commonalities, but I can't think of a single fact, belief, or doctrine that is both necessary and sufficient to define a "guerilla war"?
>How is it related to other military developments like conscription, and to political developments like nationalism and democracy?
Less than you might think. At a rough commonality, a guerilla war generally tends to try to outlast the larger, stronger, conventional force, and raise the costs of its operation higher than the conventional polity is ready to bear. While technological and social changes have altered the cost calculations, that there are operational costs and limits have always remained and almost always will remain.
>What doctrine has proven to be effective in quelling it? Has there even been one?
More bodies, better policing tends to work the best, at least in modern contexts.
Is a fabian strategy really guerilla war though? I mean, the namesake still sent out regular forces to oppose Hannibal, and while he didn't commit to decisive battles, he did essentially adopt a very Grecian style of operations, of move and fort and restrict enemy movements, as opposed to modern guerrilla warfare which ignores the enemy's movements altogether, attempting to strike at civilian infrastructure behind the army's back.
Surely Pericles had Fabius beat by about 200 years. There's little practical difference between the Athenians holing up behind the Long Walls and Fabius's shadowing of Hannibal, except that Fabius's fortifications moved around a larger area.
You can simultaneously argue that the Gureillas of the Peninsular wars weren't a "real" guerilla war since they attacked French regular forces in an attempt to drive them out of Spain, and point to things like Hebrew attacks on Roman settlers literally millenia before as demonstration that the concepts of modern insurgency existed way, way before.
What possible definition could you give of guerilla warfare that would lead to the conclusion that it started in the 19th century?