Couple of other things to add…
Ahmadi Muslims are a bit different from other Muslims in some other ways. One is that the structure and unity of the movement is truly global and not territorial, meaning that every Ahmadi (with the exception of a truly tiny splinter group) is truly one, in a way that’s similar (but not exactly the same) as the Catholic Church and its global unity, compared to other Christian churches that have a bit less of that, or quite a lot less of that. I can’t recall all the relevant terms off the top of my head, but it is one thing they like to talk about.
Ahmadi Muslims are unique among Muslims in that they have absolutely no desire for Islamic law to be the actual law of any country. They are universally on board, really on board, with freedom of religion and separation of church and state and all the rest. Truly on board, in a way that mainstream/moderate Muslims are for the most part very much not, even if they are living as a tiny minority in a very secular country. In this sense, Ahmadis are the most secular of all Muslims if you want to call them Muslims, and they are the only Islam-ish group that is truly and consistently this way through and through. Basically, they are pro-West in several very large ways, and this is one of the main ones.
Ahmadi Muslims have always been far more committed to missionary work than any other kind of Muslim. There was a concerted effort early on, still in the late 19th and early 20th centuries, when they made a point of sending some missionaries to every country in the world. Literally every one. Because of that, to this day, there are some hard-to-reach countries where the entire Muslim population is something like 12 and they are all Ahmadi. It’s also worth pointing out that they are totally against gaining and keeping adherents by way of coercion, which means they had better be very good at persuading and inviting on a regular basis. This is not much of a winning strategy in an environment where your competition is being incredibly coercive, but overall on a global scale it is working quite well in certain places. For the most part, those certain places are in Africa, where there’s a significant Muslim minority or even a majority, but those Muslims are relatively peaceful and tolerant, and they may even be fairly pro-West, so the Ahmadis have been making a fair bit of progress. Nigeria, Kenya, west Africa- actually, if you look at any of the west African countries that were hardest hit by Ebola, those are going to be your main African countries where Ahmadis have claimed a really substantial share of Muslim populations, although we’re generally looking at Muslim-minority populations where they’re having the most success.
Just one more thing- it seems to be incredibly difficult to pin down exactly how many Ahmadis are in the world, even in Pakistan estimates vary by a range up 5 million or so. It’s absurd, and there’s plenty of countries where nobody has any clue at all. Based largely on estimates though, it probably is the fastest-growing sect of Islam as a percentage of itself, unless you want to count non-denominational Islam which also seems to be quite a thing as well. The last time I remember seeing an approximation of their numbers within a list of all Muslim sects, I recall that they were just behind the Zaydis on that list, which is one of the groups currently being slaughtered and running out of drinkable water in Yemen. I think that’s the minority group, those are the Shia in Yemen, and…is the US backing them or fighting them? I’m pretty sure Iran is backing them, and the US is probably backing the other side. If I recall correctly. Of course Zaydis have absolutely nothing to do with Ahmadis, except for the fact that there are (probably) fairly similar numbers of people in each group, although Ahmadis are way more spread out.
Jews have those too, called Karaite Jews (but that movement is much older, from about 200 BC).
