[photochemsyn]

They're certainly an optimal delivery device for biological and chemical weapons, and I imagine it's only a matter of time before such programs are revived by various powers, given the current breakdown in international treaty regimes governing what I'd call the four horsepeople of the apocalypse: nuclear, chemical, biological and cyber warfare.

[sofixa]

How are they more optimal than the "traditional" (for the last few decades) method, a missile? Missiles have the advantages of bigger range, faster, different profiles (hypersonic cruise, ICBM). A drone might be harder to detect today, maybe, because anti-air systems didn't need to deal with them (while they did have to deal with missiles, so are optimised for that use case), but that's about it?

[photochemsyn]

Availability is much higher, so that opens the door to use by non-state actors. Stealth is probably also higher. I suppose the combination, i.e. missiles delivering cluster-type munitions (releasing hundreds of drones instead of hundreds of bomblets) is what state-level militaries would pursue.

Little-known fact: cluster munitions (essentially, hot-water-heater-size cylinders packed with hundreds of small devices) were originally developed for the dispersal of chemical and biological warfare munitions over wide areas.

[dmos62]

I know you were talking about conventional warfare, but unless your apocalypse-causing list includes inflation upfront, it's not complete.