It is always justified if done the proper way by the proper reasons. A military action IS justifiable to remove Omar al-Bashir. Will it be done? No. Why? No economical profit from it. There's a military action taking place in Haiti lead by the UN, a country teared apart by war, hunger and poverty. Several nations are sending in soldiers (including Brazil). American soldiers in Haiti? None. No profit from it.

So, answering your question, military actions are justified when they are done with the porpouse of saving people's lifes and making them better. WW2 for instance was justifiable. Vietnan was not.