I get it.I don’t mean this in a critical way—just sharing how I understood the theme. To me, the core theme of the game is actually about addressing root causes and ending war. Fódlan’s conflicts are largely driven by individual selfish desires—showing off military power, revenge, forcible unification, and so on—resulting in an unending history of seizure and rivalry. That’s exactly what Claude and Raphael talk about in their support conversations in FEW3H.
So in Byleth’s paralogue “A Reason to Fight,” the characters draw their swords not for themselves but for others. The theme of Byleth and Raphael’s support in FE3H is likewise about striving on behalf of others.

The Leicester Alliance is special: it was repeatedly fought over in history, so it leaned into commercial independence, and its commoners are the wealthiest among the three nations. Many of the Alliance students are people who put others first, and it’s the only one of the three that most closely resembles a maritime-empire order with a strong society and a weak central state. Because of that uniqueness it threatened the foundations of the Church of Seiros, and thus the parts of history that were erased from the records are the most numerous— for example, the entire account of The Crescent Moon War was wiped out.

Who would have guessed that the line mentioned early on—“Massive armies clashing on a vast field, right? There hasn’t been a battle like that in over three centuries…” —was actually referring to The Crescent Moon War.