In the United States and some other republics, the oath is known as the Pledge of Allegiance. Instead of declaring fidelity to a monarch, the pledge is made to the flag, the republic, and to the core values of the country, specifically liberty and justice. The reciting of the pledge in the United States is voluntary because of the rights guaranteed to the people under the First Amendment to the United States Constitution - specifically, the guarantee of freedom of speech, which inherently includes the freedom not to speak.
