It is called winner -take all system
founded on one of the fundamental principle of democracy, this system requires statesmanship from the losing candidate, a sacrifice that is not guaranteed. Most elections are bitterly contested and it is always possible for the losing side to feel disenfranchised which may lead to outbreak of clashes, as the losing side supporters feel cheated.
A typical case study is in the Kenyan election where tensions are always very high, especially when opposition leader Raila Odinga loss an election, as he is always unwilling to concede.