Welcome, Lunar Girl!
Too bad I'm your welcoming committee; I've only been around here a year or so myself.
When this thread got started there was some shenanigans with the actual stipulations. "OP," I've come to gather, can mean either "original poster" or "original post;" I've come to favor the latter theory as to its meaning. Well, the Original Post would be perfectly well satisfied by your suggestion! But then the Original Poster threw in the belated curve-ball--these Western Hemisphere Muslims were to speak English! Then the OP changed their mind again...
But meanwhile I was provoked into the amazingly convoluted scenario I evolved in the course of trying to square these circles, and reading it over I have to say I'm still pretty proud of it--behold, not only do I have a largely (perhaps entirely) Islamic Western Hemisphere, I have
1) Ireland-wanking (sort of--to "wank" a country is to glorify it beyond its Our Time Line ("OTL"--perhaps you've been lurking long enough to know all the dark secrets of the acronyms around here but it took me months, and I still may not have them all right yet) achievements and perhaps beyond all bounds of reason. While I'm not particularly attached to Hiberno-Wanking it so happens a form of this was the very topic that moved me to join and post in my first thread. I even had a basis here for the revival of Celtic-rite Catholicism. On the other hand, my Ireland-wank here involves it being an intermediary goon state for purposes of
2) England-nerfing (not sure that's the proper opposite of "wanking" but it's the one I picked up): England itself turned into a colonial hothouse of forced labor, on the land, perhaps eventually in rising (Moorish-Iberian dominated) industry, and certainly, for purposes of gratifying the OP, a source of surplus population for the Islamization of the Americas (not called that here obviously) by an English-speaking and ultimately Muslim mestizo nation. So in a sense English, as a language and cultural background, winds up nearly as influential as OTL, but it's a very different Anglo culture that fits into a very different larger world.
One that includes
3) Holy Roman Empire AND France-wanking, in the form of a forced emergency fusion of the two and consolidation of a Pan-Euro-Christendom state, except for Turkish-ruled Italy and Islamo-Iberian ruled British Isles--again this "wank" is kind of twisted since Euro-Christendom becomes a backward theocracy;
4) Ottoman-wanking, or rather (since I suggested the Point of Divergence AKA "POD") might be that some other Turks take Constantinople earlier and are thus in a position to help the Moors hold on to Iberia, thus "some-analog-to-the-Ottomans-wanking"--they don't directly control the colonization of the New World to the West but they do profit from it.
5) A suggestion of West-Africa-wanking--this would help explain why the Iberians turn north rather than south for their forced labor supply. And give the Iberians some sorts of plausible rivals--almost certainly in the context, fellow Muslims.
6) A possible Maroon state ('maroon' being a term for escaped slaves who set up a new creole/mestizo society of their own in conjunction with friendly Native peoples, something that certainly has happened historically OTL) that manages to parley itself into a first-class world power by the 20th century (Western Common Era ie AD--the Muslim people of the Atlantic would of course be using the Muslim calendar based on the Hegira and thus for them, the 13th century). It gladdens my heart to see escaped slaves making good and history rarely affords examples on a national scaleso I'm glad I stumbled into that one here! Anyway some sort of major political revolution somewhere between the 1500s and 1900s AD would seem necessary to explain an English-speaking Muslim power in the Western Hemisphere!
So this bizarre set of moving goalposts resulted in my stumbling into what I still think was an amazing alt-historical bank shot that I could hardly dare to set out to accomplish.
Well, I guess you did read it and weren't impressed, as no one else seems to have been either from the total lack of response for the past 8 months.
Your own very straightforward and simple answer to the Original Post is quite appealing as an alternate history--yet for some reason or other an Al-Andalus dominated, or even present, Western Hemisphere never seems to get much traction around here. It looks like a blind spot to me rather than something that is just plain implausible--why shouldn't the "Moors" (actually an amalgam of various Muslim immigrant/conquerors--therein may have been part of the problem, in their diverse ambitions, but perhaps also a solution) have consolidated their hold on Iberia and gone on to play a role not unlike that played by Spain and Portugal OTL? Arguments against include that OTL they were pretty poor at achieving unity among themselves (but saying "what if they did it anyway? is perfectly good AH); that even if they did secure themselves as a consolidated realm that could stand against Christian Reconquista they'd be isolated from Europe and therefore could not play the roles of Spain or Portugal OTL (but OTL Moorish Spain did have political and economic relations with Christian Europe; stabilizing itself might harm these relations and might help them; also, they have other potential partners to work with besides their European close neighbors, such as their African ones and the core of the Muslim world at the other end of the Mediterranean). So a straightforward al-Andalus more or less substitutes for the role of Spain OTL strikes me as a perfectly reasonable AH!
Again welcome!
Thanks so much for the explanations, I haven't had time to look them up yet but I know I'll enjoy it here. I read through the whole thread and no one seemed to talk about the idea of Muslims possibly keeping Spain. Plus, if they brought over African Muslims as slaves, again you would have an even bigger possibility of a majority Muslim society, since both the masters and the slaves would be of the same religion. Since the Spanish were the first to colonize, it wasn't too far-fetched of an idea to me.