How did nations participating in world war 1 control opinion? why was this important​

They used propaganda to influence people into buying into the war.

Propaganda on posters and other things to persuade the public to support the war. This way the government could collect money from the public through liberty bonds and they would follow laws supporting the war to better the war effort.

yes

explanation:

the fighting words doctrine, in united states constitutional law, is a limitation to freedom of speech as protected by the first amendment to the united states constitution. in 1942, the u.s. supreme court established the doctrine by a 9–0 decision in chaplinsky v. new hampshire.