Conflict has many origins and cannot be pinned to any one single cause. There are many deep and complex roots to conflict.
This view -- atheism as the [only-implied] 'real' force behind war -- is an absurd fabrication. The view that religion is the [only-implied] 'real' force behind war -- is also absurd. More likely, the true sources of conflict are territorial disputes, empire expansion, political agendas, personal agendas, religious/cultural differences, and mass suffering, to name a few.