1 November 1911: first recorded bomb drop from an airplane in history, by Italian Lt. Giulio Cavotti, against rebelling Arabs near Tripoli.

1912. first French use of aerial bombing, against rebellious Berbers in Morocco.

1913. first Spanish use of aerial bombing, again in Morocco.

1915-1920: first British aerial bombings in colonies, but then already at grand scale: in India, Egypt, Iran, Afghanistan, Somaliland.

1925: first total destruction of anentire town by aerial bombing, by US pilots hired out to France, against the Moroccan town of Chechaouen: holy site of the Jibala tribe, 6000 inhabitants, none armed.

Then came the bombings in Iraq - and their architect was none other than Arthur "Bomber" Harris. The terrorist total-war mindset behind firebombings (which specifically targeted civilians) weren't without precedent, without a prehistory.

The article also tracks back the ideology of total war (i.e. a war fought between 'nations' at all costs, without making difference between civilians and combattants):

1915. British mathematician P.W. Lanchester proposes the burning of entire cities as a tactic of war.
      
1918. British politician Winston Churchill proposes the destruction of Berlin with a bombing raid by 1000 airplanes. (He got that, multiple times, two-and-a-half decades later.)
      
1921. Italian General Guilio Douhet creates the full-blown doctrine of total war.