How do politicians exploit social division ?

It is generally assumed that social divisions along with politics can threaten the unity of a nation. This can be true in some cases. In democracy, many political parties contest for power. Thus, they may exploit social divisions that exist in the society for gaining their own aims. This may lead to violent protests or even disintegration of a nation.  For example, in Sri Lanka, Acts were passed by the government which gave preferential treatment to the Sinhala community over the Tamilian population.  There were a series of protests staged by the Tamils in Sri Lanka. Finally, this conflict resulted in causing a Civil War in Sri Lanka, in which millions of people lost their lives.