One can argue that the U.S. civil war was, or developed into, the first modern war, the first war that was fought in the manner that was to sadly dominate the 20th century. Maybe the ‘style’ of war has fundamentally changed again, with the fragmentation of fronts between states and terrorist groups, guerrilla warfare, or the rise of drones and similar technology, cyber warfare… As a pacifist who chose to serve in emergency medical services, I’m really out of my depth here.
Jeffery B. Roth wrote a fascinating piece on the use of biological (e.g. sending infected clothes to enemy lines) and chemical (e.g. Greek fire artillery shells) weapons in the civil war for the New York Times’ “Disunion” series.