In the beginning there were no parties and this country was a republic. The the democratic republican party came along and eventually became today's democratic party.
Republicans slowly slid towards center while democrats slid further towards communism.
http://en.wikipedia.org/wiki/Political_parties_in_the_United_States
In January 1776, just as it became clear in the colonies that the king was not inclined to act as a conciliator, Thomas Paine's pamphlet Common Sense was published.[21] Paine, who had only recently arrived in the colonies from England, argued in favor of colonial independence, advocating republicanism as an alternative to monarchy and hereditary rule.[22] Common Sense introduced no new ideas,[23] and probably had little direct effect on Congress's thinking about independence; its importance was in stimulating public debate on a topic that few had previously dared to openly discuss.[24] Public support for separation from Great Britain steadily increased after the publication of Paine's enormously popular pamphlet.[25]