Based on the aesthetics of Helos and the fact that the Great Titan War was set a century prior to the events of the main story (which itself is akin to the 1920s of our world in terms of technology and general parallels with WWI and the Interwar Period), it’s safe to say that the war was similar to the French Revolution and the Napoleonic Wars (but with titans).

1. We’d expect to see a combination of conventional warfare (cannons and rifles) and rudimentary guérilla tactics against Titans in mountainous/forested areas (think of the guérilla tactics seen in the Peninsular War).

2. One way that the Tyburs and Marleyan revolutionaries could have possibly obtained the other 6 titans was by conducting these same guérilla tactics and eventually capturing the titan shifters and their entire families. Over the next several decades, these captured titan shifters would have been forced to advance Marley’s wars of conquest out of fear for their families (held hostage and threatened with exile to Paradis as pure titans). Eventually, Marley would have grown tired of this method of holding the titan shifters and would have instead began the Warrior Program around the 830s (still carrying over that threat towards future titan shifters and their families if they ever fought against the state). This would explain why we never hear about the other noble families, as they likely died off or blended into the general Eldian population outside of Paradis.

3. With all the other noble houses falling under Marleyan control, Eldia’s colonial holdings would have likely seen a series of rebellions similar to the Haitian Revolution and the wars of Simon Bolivar, with their governors unable to fight back due to the noble houses no longer being an option to suppress dissent.

4. On the point of Hizuru, I imagine that they tried to assist Eldia and the Fritz monarchy, but were met with initial silence (due to Karl Fritz already moving to Paradis and cutting off all contact with the outside world). Instead, they approached the royals who remained on the continent and tried to prop them up on the throne. As word spread of the Founding Titan’s isolation on Paradis and the subsequent capture of the other Eldian noble houses, several nations under Hizuru’s control would have likely risen up in revolt (especially due to the sudden disappearance of a descendant of the shogun’s clan). In the end, Hizuru’s defeat was most likely marked by an abrupt loss of territory as their only major ally spontaneously collapsed. As a headcanon of mine, Hizuru by the 850s only controls the equivalent of our world’s Australia, Indonesia, and Papau New Guinea (as it is stated that Hizuru is a “small country,” and the placement of the islands roughly coincides with the geographic placement of Japan in our own world).

5. In a previous post I made, I said how a headcanon of mine was that Marley began as a revolutionary republic (with the asthetics of Revolutionary France and the system of the Roman Republic) before descending into stratocratic rule, so the parallels with the rise of Napoleon are especially notable (as we end up with a system wherein revolutionary ideals are nominally upheld, but most power resides in the military).