Party identification is the single most important predictor of how people decide to vote because

Because it specifically impacts one's vote and indirectly colors the partisan's impression of issues and candidates. 
Party identification alludes to the political party with which an individual recognizes. It is being loyal to a political party which is usually controlled by the political party that an individual most generally supports by voting or different means.

My best answer is the haudenosaunnee or the iroquois.