The enmity between the Reach marcher lords and the Dornish (e.g. Oakheart and Darkstar) seems unusually fierce given that they’ve been at peace for over 100 years. Do you think there’s been border raids etc over that time (and wouldn’t that be illegal/treasonous?) or is it just another example of long Westerosi memories and stasis?

There have absolutely been border raids: “the castles of the Dornish Marches are among the strongest of the realm, and for good reason, for seldom has a generation passed when hey have not faced some new attack…even during times of peace, raiders out of Dorne continued to descend from the Red Mountains in search of plunder.” But I’m highly amused at the idea that 100 years of peace means that enmity is unusual. 

We’re talking an enmity built over thousands of years of conflict. The very identity of the marcher lords of the Reach and the Stormlands is built on defending their land from (mostly Dornish) border raiders – you think the Carons forget that the Fowlers burnt their castle in 9AC? You think the Hightowers forget the Daynes burning everything outside the walls of Oldtown twice? Going further back, you think anyone in the Reach would forget that the Dornish sacked Highgarden, burnt the Oakenseat, and murdered Garth X in his bed? Over in the Stormlands, the castle of House Swann is built practically on the spot where the Yronwoods and Wyls were stopped in a battle so bloody it dammed the river Slayne. 

Also…100 years of peace is a bit of an exaggeration. Less than 10 years after Dorne entered the realm, you had the Blackfyre Rebellion (which as my forthcoming Tower of the Hand essay will point out, largely focused around Dorne), which Dorne fought in for at least three of the conflicts. Maekar died fighting in a rebellion on the Dornish Marches in 233.