" As a global phenomenon, Christianity is by no means withering away under the assault of modernization; the only exception is Europe, where Christian decline is the rule. The not-so-good news, from the point of view of Matthew 28: 19 and the "Great Commission" ("Go therefore and make disciples of all nations..."), is that Christianity's impressive absolute growth in the last century is not matched by its relative growth: Christianity claims a slightly smaller percentage of world population today than it did in 1900.
Indeed, Christian growth in Africa is nothing short of astonishing. There were 8.7 million African Christians in 1900; there are 389 million African Christians today; and Barrett projects almost 600 million African Christians by 2025 (when Europe's Christian population will have fallen to 513 million). "
That's probably not that telling of a stat. I think India and China are a substantially larger chunk of the world's population now than they were in 1900, and neither nation has many Christians ... yet. ;-)