How did the Great War affect American ideas on liberty?
At the time of the Great War, most Americans drew no distinction between nationalism and liberty. The ideas of progressivism which had dominated American politics were soon equated with "Americanism." Woodrow Wilson once commented
Once lead this people into war, and they’ll forget there was even such a thing as tolerance.
Intolerance became manifest in attitudes toward anything German. Schools refused to teach the German language, orchestras would not play music by Beethoven or Mozart Sauerkraut became "liberty cabbage," and German measles "liberty measles."
The most pronounced incidents of nationalism over personal liberty was expressed in the Sedition Act of 1916 which made it a crime to utter or publish anything
disloyal, profane, scurrilous, or abusive about the American Government, Constitution, Army, or Navy.
Later, Congress passed the Espionage Act of 1917 which provided stiff prison terms for statements deemed to instigate disloyalty or give aid and comfort to the enemies of the U.S. The constitutionality of the law came before the United States Supreme Court in Schenck vs. United States. In upholding the law, Chief Justice Oliver Wendell Holmes Jr stated:
The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic. [...] The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent.