The promises that you make upon citizenship are: give up loyalty or allegiance to other countries, to defend the Constitution and the laws of the United States, to obey the laws of the United States, to serve the country in the armed forces if needed, to serve the country when and if required and to be loyal to the United States.
When the United States became an independent country, the Constitution gave Congress the power to establish a uniform rule of naturalization. Congress made rules about how immigrants could become citizens. Many of these requirements are still valid today, such as the requirements to live in the United States for a specific period of time, to be of good moral character, and to understand and support the principles of the Constitution.
After an immigrant fulfills all of the requirements to become a U.S. citizen, the final step is to take an Oath of Allegiance at a naturalization ceremony.