Social exclusion leads to despair and alienation. If people are excluded from society, then it is no wonder that they turn to violence. There is no civil war in any country which has full employment. If work for all who need it is a basic feature of maintaining stability in a society at peace, then it must also be an objective for reconstructing a society after a conflict. After all, ex-fighters need to be given an incentive to help rebuild society.
Peace brings the risk of losing that status - and the prospect of unemployment.
Work will enable them to achieve social inclusion. Additionally, combat is an energetic activity. These ex-fighters will have a lot of energy to redirect. Work will absorb all that energy. Local reconstruction programs will also help ensure that money will be spent in the local community by the local former combatants.