Religious fights in the 21st century?

And recently in the Assam province of India, clashes between Muslims and the indigenous Bodo tribe turned into a massacre when 87 people were brutally killed, 14,000 houses were burnt down. What is the reason behind such ethnic and religious conflicts becoming more widespread? Why do people who had been living together for centuries start to behave like enemies all of a sudden? One of the reasons is that the religious, ethnic and sectarian sense of belonging has come to the forefront more, leading to rivalry and conflicts among different groups in a country.