Democracy involves competition among various political parties. Their competition tends to divide any society. If they start competing in terms of some existing social divisions, it can make social division into political division and lead to conflict, violence or even disintegration of a country.
Hundreds of civilians, militants and security forces were killed in the fight between Unionists and Nationalists and between the security forces of the UK and the Nationalists. It was only in 1998, that the UK government and the Nationalists reached a peace treaty after which the nationalists suspended their armed struggle.
Political competition along religious and ethnic lines led to the disintegration of Yugoslavia into six independent countries.
In a democracy, it is only natural that political parties would talk about the social divisions, make different promises to different communities, look after due representation of various communities and make policies to redress the grievances of the disadvantaged communities.
Social divisions affect voting in most countries. People from one community tend to prefer some party to others. In many countries, there are parties that focus only on one community.