I don’t think 200 years ago is enough time. Humans already had centrally fortified positions (castles), cannons, guns etc. heck the Gatling gun was already 162 years ago. You need to go further back but that would likely just extend the inevitable as humans extend their technological advantage where the elephants aren’t (eg colder climates which is where a lot of tech advancement happened). So for them to actually defend against humans they’d need to similarly be able to do tech which their morphology prevents them from engaging in really. There’s also the other problem that they’re territorial but not expansionist. They’re not like lions that capture and defend large swathes of territory either. They just protect their herd / fight elephants for territory which makes sense because they’re not predators like we are. In other words, not only do they need richer communication to organize (which arguably they probably do to some extent), they need to have a complete change in how they’ve evolved to think about the world in terms of hunting like a pack / developing military strategy. Humans are annoyingly adaptable and dangerous and will adapt military techniques (and by the 1800s we’ve had millennia of fine tuning armies)