Just War Theory is a philosophical framework that seeks to ensure war is morally justifiable through a series of criteria, balancing the need to protect the innocent and uphold justice while minimizing harm and destruction. It is divided into two main parts: 'jus ad bellum', which outlines the conditions under which it is permissible to go to war, and 'jus in bello', which dictates how war should be conducted ethically once it has begun.