Buddhist nation that have engaged in wars,but never for the sake of Buddhism itself.Only for the greed,hatred,jealousy etc...which is universal to all human beings,irrespective of religion.
Human beings,being what they are,incidents of greed and anger among the unenlightened.Buddhism probably has the fewest incidents of oppressive behavior among it's followers.
Soldiers in the Buddhist religion are actually noble people,but they are still affected by karma.They will still be affected by negative karma for taking a life.Soldiers are looked upon as a noble because they sacrifice their lives and their karma for the sake of protecting others.Buddhism does not condone violence and have an army,but only for DEFENCE.