Whatever the case may be in the evolution of Empire, at least during the times of Italian expansion the Romans were indeed interested in making sure their war was just in the eyes of the gods.

"Since Numa had instituted religious practices in time of peace, so Ancus Marcius provided a ceremonial for war that wars might not only be waged but also declared with some form of ritual. So he adopted from the ancient people of the Aequicolae the law that the fetials now have by which a state demands redress for an act of hostility. When the legate arrives at the frontier of those from whom redress is demanded, he covers his head with a woolen cap and says: 'Hear, Jupiter, hear, boundaries of ___ let divine law hear! I am the official herald of the Roman people. I come in the name of justice and religion; let there be trust in my words.' Then he recites his demands. Next he takes Jupiter to witness: 'If I unjustly or impiously demand that this property and these men be surrendered to me, then never let me have enjoyment of my native land.'

He recites these words when he crosses the boundary line, again to the first person he meets, again when entering the town gate, and again when he has entered the market-place, with only a few changes in the formula and wording of the oath. If his demands are not met at the end of thirty-three days (for this is the conventional number), he declares war as follows: 'Hear Jupiter and you gods of the underworld, hear! I call you to witness that this people ____ is unjust and does not make just reparation. But regarding these matters we will consult the elders in our fatherland, how we may obtain our due.' Then the legate returns to Rome for the consultation."

-Livy 1.32.6-14