The historian monk Matthew Paris wrote that King John offered to convert to Islam in return for military aid from Muhammad al-Nasir. I gather this is not thought to be true. So was this anti-John propaganda, a genuine error or something else?
Is this, given this was the time of Crusades against that ruler, an early example of Islam being regarded as a threat at home as well as abroad?
Very likely pure propaganda, but it raises a lot of interesting questions.
John was a heinously unpopular ruler with the chroniclers, and Matthew Paris certainly isn't the only writer who looked down on him. The early 13th century chronicler Layamon, who probably lived during John's reign, wrote a Brut chronicle including the life of King Arthur as he imagined it. Layamon's Arthur acts a certain way in a few key scenes in the narrative that look suspiciously like direct contrasts to how John behaved through his reign. For instance, Arthur grows pale and weeps when he learns that his father has died, while John reportedly showed terribly little emotion when he got the same news. Arthur was generous and fair with all his subjects, while John was notorious for levying scutage much more than his predecessors. You get the idea. At best, it was an instructive model for nobility, or at worst a subtle joke at John's expense. Roger of Wendover was another chronicler who described John's troops in the north as "devil-like locusts." All that to say, both the powerful St. Albans where Roger of Wendover and Matthew Paris were writing and the humble Areley Kings where Layamon was writing didn't have much love for King John in their writings. When these chroniclers wrote their histories, while some were more responsible for others, spinning facts (or outright making them up) was common to the point that it was basically tradition.
All that to say that considering the times, it's relatively believable that Paris made this up, especially considering that it involves an unprovable expedition to a far-away land for an outrageous proposal. I'd be hesitant to say this is an example of a "red scare" style Islamaphobia at home, though. I'm no religious historian, but from what I can tell, Islam at this time wasn't regarded so much as a polar-opposite ideology as much as it was seen as the exotic 'Other'. My mind jumps to Palomides, a Saracen character in Arthurian romance literature who converts to Christianity and becomes a heroic Christian knight with the rest of them. Palomides is presented as a character who follows the romantic Christian traditions to a T, to the point that he doesn't quite understand the spirit of it all, and he's frustrated by unrequited love for the Christian Isolde, ending up as the third wheel to the born-and-bred Christian Tristan. It's an Orientalist trope, the character who totally adheres to a lifestyle but doesn't 'get' it, but it doesn't read the same way the "threat at home" trope does. Islam was foreign enough to England that they were more likely to see Islam as an entirely foreign identity rather than as something subversive that could make Christians convert at home in the same way they thought different vices could corrupt them. Similarly, in England's own Jewish communities, you were much more likely to hear about blood libel than you were about Christians at risk of converting to Judaism. In that sense, when Matthew Paris writes something as audacious as this, it's probably more a commentary on King John's weakness as a ruler, that he would offer himself up to a fundamentally foreign entity for help.
As for any actual historicity, I can't find any scholarly sources who've really looked at this. You might look for evidence or lack thereof in the pipe rolls (records of the Exchequer) to see if there's any records of envoys heading East, but the fact that there isn't any other conspicuous evidence available or retellings in later chronicles are a hint that Paris probably made this up, or at the most, extrapolated an incident of contact with a Muslim ruler. I'm sure that's not a satisfactory answer, but from what I can tell, this is a foggy entry that few people have done peer-reviewed work on, so the best I can offer is a little context!
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