How will the US force people in other countries to use communications which it is known the US can decrypt?
By making the likes of Huawei an offer they can't refuse, and then escalating if they try to refuse.
We've seen they how the UK government was on the point of reaching a sensible decision, but an agent within it (possibly Williamson) was able to scupper that. Vassal states do what we're told, and US sanctions have a long reach.