The Democrats and Republicans make up what system?

"The two-party system" is the answer you are supposed to give. But you are smarter than that. In fact the United States has seen plenty of political parties at the national level. Before the election of Abraham Lincoln there were four parties trying to gain the Presidency. The two-party system is a myth created by lazy text book authors who can't find the time to explain things properly.

The Constitution provides for no political parties. And the founding fathers were not enthused with their development. But political parties formed none the less. And they continue to form in the modern era of our nation. Popular Libertarian Ron Paul has run as a Libertarian and has sought the Republican nomination for President.

So spend some time studying up on our American political parties. And beware of people who tell you that a Democracy and a Republic are two different things.