The correct answer to this open question is the following.
The concept of representative democracy in the United States started with the creation of the US Constitution during the Constitutional Convention in the city of Philadelphia, Pennsylvania during the summer of 1787. Delegates met to discuss the new form of government after the Articles of Confederation had left a weak central government that couldn't collect money through taxation or organizes an army.
Here, the founding fathers opted for the principle of Republicanism, in which the citizens can elect their representatives to create laws that help the nation to progress in peace.
America is a representative democracy in which its citizens are able to participate in elections to choose small groups of people to make laws and policies for them.
For that to happen, political parties choose their candidates that compete in elections.