Answer by taking a quote from the following article:

Junius Richard Jayewardene (Sinhalese: juniys ricdd jyvrdhn,Tamil: juunnniys ricctt jyvrtnnnaa; 17 September 1906 - 1 November 1996), commonly abbreviated in Sri Lanka as J. R., was the leader of Sri Lanka from 1977 to 1989, serving as Prime Minister from 1977 to 1978 and as the second President of Sri Lanka from 1978 till 1989. He was a leader of the nationalist movement in Ceylon (now Sri Lanka) who served in a variety of cabinet positions in the decades following independence.

On the economic front, Jayewardene's legacy was decisive. For thirty years after independence, Sri Lanka had struggled in vain with slow growth and high unemployment. Since Jayewardene's reforms, the island has maintained healthy growth despite the civil war.  On the ethnic question, Jayewardene's legacy is bitterly divisive. When he took office, ethnic tensions were present but the country as a whole was at peace. By the end of his tenure, Sri Lanka was facing not one but two civil wars, both featuring unprecedented levels of violence and brutality.  Though Jayewardene indeed did not take measures to stop the attack on Tamils, he was not opposed to them personally, only politically. One of his most esteemed friends was a supreme court judge of Tamil ethnicity, a member of an elite family and raised in Colombo, but who was strongly linked to his Jaffna Tamil heritage. This is but one close Tamil friend of the president's, and it is quite clear that he was not a racist but rather a man who knew how to exploit racism to win the majority.  Highly respected in Japan for his call for peace and reconciliation with post-war Japan at the Peace Conference in San Francisco in 1951, a statue of Jayewardene was erected at the Kamakura Temple in the Kanagawa Prefecture in Japan in his honor. In 1988, the J.R Jayewardene Centre was established by the J.R Jayewardene Centre Act No. 77 of 1988 by Parliament at the childhood home of J. R. Jayewardene Dharmapala Mawatha, Colombo. It serves as archive for J.R Jayewardene's personal library and papers as well as papers, records from the Presidential Secretariat and gifts he received in his tenure as President.

what was the civil war about?
When he took office, ethnic tensions were present but the country as a whole was at peace.