What Daeron I did wrong? What misstep he did that avoided will free us from the canon Conquest?
Marching an army into the desert. It's always the same shit, always with the Reach armies marching into the desert...
Basically, both Aegon I and Daeron I's second campaign treated Dorne like a normal campaign in any other part of Westeros. You amass a big ass army, and then march from hold to hold and force them to surrender. Only in Dorne, holds don't stay surrendered, but will rise up again as soon as the host marches on, and also the desert means you can't "forage" making the logistics of your big ass army very difficult.
So... don't do that.
While I am not necessarily in favour of it, I think a more successful Conquest of Dorne
could be done. Treat it as a naval operation. Dorne has so much coast, but basically zero naval power (and in the rare times they do, well, the Fourth War is a lesson of what happens to enemy ships under dragon fire). Assemble a fleet in the southern Stormlands, and then land at the Arm of Dorne and Sunspear. A safe crossing should be assured; the Sea of Dorne between Stormlands and Dorne is even noted as a very calm sea.
So - take Sunspear
first of all instead of making it the crowning conclusion of your campaign like Daeron II did, or even sparing it in order to incite an anti-Martell revolt as Aegon I did.
Decapitate Dorne. And then don't march into the desert, but first secure coastal Dorne. Lock that shit down. And then you can begin a small-scale war for the desert, basically taking one oasis at a time, many small scale operations, instead of having a big ass army marching through the dunes.
It would take time, of course, probably our whole reign would be spent keeping an eye of Dorne and it would take generations until the desert is fully pacified - but we would have the richest parts of Dorne locked down and have a road to full success, and a small scale warfare also means it would be done without too much resource investment.
