Prior to Fire Emblem: Shadow Dragon, the Fire Emblem games that came out before it — Fire Emblem GBA, The Sacred Stones, Path of Radiance, and Radiant Dawn — had characters with basic personalities that in a wartime setting and the idea that you can’t bring them back into battle made you care enough about them that you had to keep them alive. Even if it was someone like Fiona.
I’m guessing this was also the case in prior Fire Emblem games, or the ones stuck in the Land of the Rising Sun. You know, Gaiden, Genealogy of The Holy War, Thracia 776, and The Binding Blade. Heck, even Ankoku Ryuu to Hikari no Tsurugi and Monshou no Nazo valued the idea of saving your characters, even if it wasn’t as fully released as the games after those two.
Shadow Dragon teaches you death is a legitimate strategy, and fuck keeping your characters alive, in the prologue.