Final answer:
The clear and present danger test limited the speech of individuals who posed a threat to the security of the United States or its people, particularly during times of war.
Step-by-step explanation:
The clear and present danger test that was established in the early twentieth century limited the speech of individuals who posed a threat to the security of the United States or its people. This test was invoked during times of war, such as World War I, to restrict speech that could potentially harm the nation, its military forces, or its people. The test was established in the landmark case of Schenck v. United States in 1919, in which the Supreme Court ruled that Charles Schenck's distribution of literature discouraging young men from resisting the draft presented a clear and present danger and was not protected by the First Amendment.