There are Mormons outside America?
I agree it's not "spreading" per se, but their numbers are respectable among proselytizing religions today. When Islam reached a 1.8% growth rate in the 2000s we were inundated with proclamations that it was the fastest growing religion in the world (eg: https://foreignpolicy.com/2007/05/14/the-list-the-worlds-fas...).
This article from 10 years ago reports that 56% of Mormon live outside the US and Canada at that time- https://www.deseret.com/2013/8/30/20524833/the-majority-of-m...
Mormon membership numbers of actual adherents are likely 20% to 40% of membership claimed based on "inactivity" rates (and people leaving).
Samoa is a big one I guess.