What is just war according to just war theory?

As far as I understood from the books, just war has three characteristics. First, in theory, war can be justified when self-defense is needed against unjust enemies. Second, war can be justifies when conducted in a just way. These two are traditional components of just war, and they can be rephrased into “why” and “how” nations engage in war. In addition to these two, focus on post-war efforts is also arising. Therefore, justification of war, process of war, and post-war efforts are often considered when discussing just war theory.