Democracy works best when people in society disagree on a range of issues.  If one issue, an obvious example of this would be ethnicity, dominates in a country, than election outcomes will be the same each time and the government will either be paralyzed or permanent winners and permanent losers will emerge.  When this happens, democracy falters because, in the former case, the state is immobilized, and in the latter case, the permanent losers see no democratic way out of their condition.  Iraq, Bosnia and Lebanon are all examples of countries where ethnic identity has held sway as the major issue which determines how people vote.