The United States of America has been a democracy since its independence. From our first presidential election in 1788, democratic voting has been a fundamental part of the American political system.
Each branch of the US government is interlocked with each other and this is integral to having a functional democracy. For instance, we vote for our president, who appoints various federal officers, who must all get approved by the Senate. A three-branched system that prevents any single person from having absolute power. Without this, a democracy cannot last.
Democracy allows everyone to have their voice be heard. Whether poor or rich, man or woman, etc. we all get a vote in a democratic society. Although the US admittedly has a history of disfranchisement, democracy helps prevent oppression by leveling everyone out at the polls, no one person's vote means any more than another.