“What was the object of gathering … the people of God in any age of the world? … The main object was to build unto the Lord a house whereby He could reveal unto His people the ordinances of His house and the glories of His kingdom, and teach the people the way of salvation. … It is for the same purpose that God gathers together His people in the last days, to build unto the Lord a house to prepare them for the ordinances and endowments, washings and anointings.”
Keep that in mind, and consider Bruce R. McConkie, 1972:
“[The] revealed words speak of … there being congregations of the covenant people of the Lord in every nation, speaking every tongue, and among every people when the Lord comes again. …
“The place of gathering for the Mexican Saints is in Mexico; the place of gathering for the Guatemalan Saints is in Guatemala; the place of gathering for the Brazilian Saints is in Brazil; and so it goes throughout the length and breadth of the whole earth. Japan is for the Japanese; Korea is for the Koreans; Australia is for the Australians; every nation is the gathering place for its own people.”
There must, then, be a clear correlation between the spread of temples around the world, and the spreading of the Church around the world. I grabbed the list of temples and plotted when they opened:
The graph starts with the 5th temple, Laiee, Hawaii, in 1919; Excel doesn't like dates before 1900, and the rest of the graph illustrates the point. The Bern Switzerland temple (#9, 1955) was the first temple built outside of North America. (The first outside the US was #6 – Cardston Alberta, 1923.) It was shortly followed by Hamilton New Zealand (#11, 1958) and London England (#12, 1958).
In the early 80s, the number of temples doubled. This makes sense, given that in 1978, the Church suddenly found itself with a lot more members who could go to the temple.
The number of temples doubled again in the late 90s. (This is where the line goes straight up.) President Hinckley announced the new, smaller temple format and that they'd be doubling the number of temples in operation by the end of the millennium. It took just over three years.
There are currently 129 temples in operation, and another 16 have been announced or are under construction.
