For centuries, Christianity was a pacifist religion. But the deeper Christianity got invested in the Roman empire, the more they wanted to protect it. This is the story of how a great thinker Christianized war for almost 2000 years.
This is a complicated and difficult topic. Many Christians fully support Augustine’s position as the correct one. This is not meant to be a discussion on the relative merits of the Just War Theory, but simply pointing out that it was not always the case.
The footage of President Bush addressing the nation is property of CBS, link here for the original video: https://www.youtube.com/watch?v=2zT-ZHBbOzM
For more information on the militarization of Christianity, you can download a pdf of an article I wrote as student about 15 years ago: http://didache.nazarene.org/index.php/volume-5-2/722-didache-5-2-military-model
For a very short look at Augustinian thought on the subject, see here: https://oregonstate.edu/instruct/phl201/modules/Philosophers/Augustine/augustine_justwar.html
For President George H.W. Bush directly citing the Just War theory as justification for the first Iraq War, see here: https://www.deseretnews.com/article/144268/US-IS-FIGHTING-A-JUST-WAR-BUSH-SAYS.html
If you still want to read more on it, there are numerous books on Augustine and his writings, but a short while still excellent book on the subject and time period is The Catholic Church by Hans Kung.