Clearly from that JW post the answer is, YES, war can be justified, so much so that God will start one and Jesus will lead an army. This is refering to a spiritual war but let us play along.
------------------------
The ancient nation of Israel served as a sample from among mankind of how God deals with obedience and disobedience. They were given laws to guide them.
Psalm 147:19 He declares his word to Jacob, His regulations and judgments to Israel.+20 He has not done so with any other nation;+They know nothing about his judgments. Praise Jah!
They had a human king and physical borders that Jehovah protected when they were obedient to his requirements. They were to war against any nation that sought to interfere in their theocracy. The Christian congregation, on the other hand, has no borders, and its members can be found in all lands. So if Christ’s followers in one country were to join in warfare against another country, they would be fighting against fellow believers.
Jesus said: “My Kingdom is no part of this world.+ If my Kingdom were part of this world, my attendants would have fought that I should not be handed over to the Jews.+ But as it is, my Kingdom is not from this source.” -- John18:36
