Concept of Karma in Bhagwad Gita and Buddhism
Bhagavad Gita is different to Buddhism because Bhagavad Gita teaches a person can kill in war without attachment. Buddhism does not teach this because any view that believes war is duty is attachment. 

In Buddhism, there are four types of attachment: (i) sensuality; (ii) views; (iii) precepts &amp; rituals; &amp; (iv) self-views. The view that 'war is duty' is attachment. 

In Bhagavad Gita, Arjuna had the view or idea of "my family" or "jati". 'Jati' (self-identity; social-identity; caste) is attachment in Buddhism. Buddha taught attachment (upadana) is the condition (paccaya) for becoming (bhava), which is the condition for birth (jati).

The Buddha ended 'jati' ('birth') therefore had no caste &amp; no caste duty. The Buddha renounced his warrior caste, unlike Arjuna, who did his warrior duty of war &amp; killing commanded by Krishna. 

In Buddhism, the noble eightfold path is the ending of kamma. By following the noble eightfold path, an arahant (Buddha) cannot kill a human being. 

The killing Krisha recommended &amp; Arjuna performed is a crime in Buddhism. If a Buddhist monk recommends to a person to kill another person, this monk is defeated &amp; immediately not a monk.

This is the difference between Buddhism &amp; Bhagavad Gita. In Buddhism, a Buddha/arahant cannot kill or teach another to kill. 


  Just this noble eightfold path — right view, right resolve, right
  speech, right action, right livelihood, right effort, right
  mindfulness, right concentration — is the path of practice leading to
  the cessation of kamma.
  
  Nibbedhika Sutta