Modern warfare is warfare that diverges notably from previous military concepts, methods, and technology, emphasizing how combatants must modernize to preserve their battle worthiness. As such, it is an evolving subject, seen differently in different times and places. In its narrowest sense, it is merely a synonym for contemporary warfare.
In its widest sense, it includes all warfare since the "gunpowder revolution" that marks the start of early modern warfare, but other landmark military developments have been used instead, including the emphasis of artillery marked by the Crimean War, the military reliance on railways beginning with the American Civil War, the launch of the first dreadnought in 1905, or the use of the machine gun, aircraft, tank, or radio in World War I.
In another sense, it is tied to changing conventional warfare, including total war, and industrial, mechanized, and electronic warfare. It can describe warfare resulting from the use or threats of weapons of mass destruction, including chemical, biological, radiological, and nuclear warfare. It can describe asymmetric warfare, involving violent non-state actors, guerilla warfare, low-intensity conflict, and counter-insurgency. It can also describe the expansion of warfare to new domains, including space warfare and cyberwarfare, as well as psychological warfare and information warfare.