Land combat was revolutionized by the introduction of trench warfare during the Civil War, and popularized during World War I. From the trenches came the long trenchcoat, as well as the quickly-formed foxholes. A doughboy might go over the top into the dangerous no-man's land under cover of a smoke screen and camouflage, braving land mines and a barrage of machine gun fire in order to carry out sabotage, or settle down in their dugouts behind barbed wire at risk of being attacked by shock troops with tear gas or mustard gas, at which point they would hope the weapons were duds and don their gas masks from their kit bags.
Back home, the talk of neutrality and preparedness could be overhead on the streets of any city. The Allies, or the Big Four, needed the help of their citizens in the war to end all wars against the Central Powers found overseas. A loyal supporter would buy liberty bonds, whereas a slacker would hide from the draft in shame.
According to I Hear America Talking by Stuart Berg Flexner, some other words that came into the language or were more used during this time are as follows:
Air/naval warfare:
After many a weary year, the soldiers began to flood back home. While a few returned with war brass, many suffered from shell shock and countless others with physical wounds (for example, basket cases (quadruple amputees)). The Treaty of Versailles demanded reparations for these ills. In memory of those who died, the United States declared Armistice Day a national holiday (later replaced by Veterans Day), and the Tomb of the Unknown Soldier was erected. The Great War was over.