The United States holds elections to elect its government leaders. The country is considered a democracy, which means that candidates are chosen by the people to fill a position rather than being appointed based on their heritage.
For many years, kings ruled over much of the world. A man was given the title of king because he was the descendant of a king or married into a royal family. The people had no say in who was their monarch, what policies were being made or what was being done in their country overall. Eventually, the people of America realized that this was not a fair way for a country to be run and developed a government of democracy. Democracy allows the people in a community to vote for leaders to represent their interests in the government.
Unlike kings, the President of the United States is in no way above the law. In addition to answering to the people in the form of elections, a president faces the risk of impeachment and removal from office if he acts inappropriately. A true monarch cannot be peacefully removed from office or voted out of his title. The people living under monarchs have no power.