During the industrial revolution kings still ruled nations. Aristocrats had concentrated wealth. People went to war when the royals ordered them to. Even France had the Bourbon restoration, though Napoleon as Emperor had taken over from nascent democracy. Germany didn't have its revolution until WW I was about lost. Except for American intervention, Crown Prince Ruprecht's final offensive would have clinched victory for the Kaisar. The Franco Prussian war of 1874 was the real stimulus for modernization of continental military technique.
The US civil war was largely one of an industrial zing north versus a lagging behind agrarian slave labor driven oligarchy.
Ortega y Gasset published The Revolt of the Masses in 1930. He anticipated two wars. He basically predicted the second world war and Spanish civil war because of social changes stimulated by mass production.
Upgrades in technology made competition for mass military equipment production keen. Military industrial complexes haven't ever really got out of the business of war. American military arsenals (and others) need to be spent periodically and replaced with new equipment via a war somewhere or production lines and sales are idled.
