What strength Christianity has in Africa, India, Indonesia, and China today is largely a post-decolonization phenomenon to the extent that Christianity transitioned from being the religion of the colonizer to the religion of some of the people.
To some degree - but there is a danger in overstating it.
Some numbers here help make this point. Subsaharan Africa had about 1 million Catholics in 1900. By 1960 - when decolonization was just getting underway in earnest - this number had surged to over 30 million. Today, it's about 200 million.
The post-1960 surge is certainly impressive, but it represented an extension of a big growth curve already in place. Independence, and the establishment of indigenously administered local churches (which the Vatican worked to put rapidly in place in the 1950's and 1960's) certainly accelerated evangelization in many areas.
Of course, both pre- and post-1960 growth owed a great deal to simple population growth. It's also true, however, that evangelization was aided by the establishment of infrastructure in these areas, during colonial rule and after. It's hard to evangelize people you cannot even travel to meet.
I am less familiar with Protestant/evangelical data here, so I don't want to generalize this to them overly.