Q: Who gave the theory of international law of war ?

Ans: The Romans have given the theory of International law of war . The credit of laws of war is given to Romans.

Romans deserved the credit for developing the laws of war. According to them, there were two types of war:
1. Just
2. Unjust

Termination of war is possible in two ways according to Romans  : 

1.Through treaty of peace
2. Through Conquest and Annexation(CA)

Categories of treaties according to International law of Romans:
1. Treaty of friendship
2. Treaty of Alliance
3. Treaty of Hospitality

Friendship, Alliance,  Hospitality. 

Friend alla hospital se.