A seminal work in anthropology, The Gift was originally published in 1923. Marcel MAUSS describes the exchange economy and the morals underlying gift-giving in archaic societies and shows that gift-giving comes with an obligation to return.
This observation is in so far relevant for understanding terrorism as it describes the underlying principles of exchange. Thus, if a suicide bomber is willing to give his life ("for the cause of God") as a gift and his enemy is not, it results in the enemy staying morally indebted to the suicide bomber. And this again plays out in the fighting spirit of the (ir)regular military forces facing each other.