[@Willy Vereb] Basically instead of the black death rampaging across Europe and killing in excess of 25 million people during the mid 14th century anyone that had it and could make the exodus to Spain did so, chasing rumors of a cure. With the French border being the only land route into Europe the (In this revised history) much stronger nation enforces a quarantine. What little trade trickles in and out of Spain travels through lazarets--ships permanently at anchor--where they are harshly disinfected, lowly Imitadores the only couriers tasked with these routes (since they can survive the decontamination and are less likely to spread the disease) Portugal is the nation most at risk, since despite Spain's best efforts and honest attempts at imprisoning their populace illegals continue to chip away at their neighbor. Those that catch the plague inevitably seek salvation in Spain, so in essence the nearby nation is being converted rather than conquered. France is nowhere near as vulnerable, a fiercely guarded stretch of 'no-man's land' between the two nation. If someone decides to be France I'll let them decide what this chokepoint is, but I'm thinking they either resorted to a huge wall or allowed violent monsters or sub-humans to settle it as a buffer. Maybe they even used magic to create a confusing fog, vigilant golems or deadly swamp.

Spain is on the verge of a crisis, as it can't sustain itself and continues to receive criminals, lepers and other such unwanted refugees (One of their biggest imports, many nations willing to pay to be rid of them in a manner that saves face) That's why so much power rests with the Fraternidad de Médicos, the masses still hold out hope that the plague can be eradicated and that they might be properly cured. Revered as they are this cabal of doctors and mystics has its own agenda and the fate of the Segremony depends on outside influences. Perhaps they can negotiate for more land, becoming a vassal nation (But whom would risk it? And why?) Perhaps they are ignored and tensions allowed to boil over, leading to civil war? Will foreign powers support or depose the isolationist king? If the black death begins to spread anew it would not only weaken some very powerful nations but provide the perfect catalyst for a righteous genocide. The disease has a face now, and that face is Spain.