I looked at the projected growth rates of Christianity by country based on data from the World Christian Encyclopedia/World Christian Database. To determine whether Christianity is growing or shrinking in individual countries, we need to look at two factors:
Let's consider a number of scenarios (I won't list all of the specific countries because the data is proprietary to WCE/WCD, and also the list would be too long):
1. Pop+/C+/Pop Greater. This is by far the most common scenario. In 154 countries, the net change in population and Christianity are both positive (both are adding people), but the population's annual change is greater. The largest example is India: the population is adding 61.6 million per year, and Christianity is adding about 1.4 million per year. The exact rates of change can determine whether % Christian increase or shrinks; in a little over half the countries, % Christian is projected to decrease.
2. Pop+/C-/Pop Greater. In 36 countries, the population is growing while Christianity is shrinking. The largest example is Turkey, where the population is growing by 20,000 per year, while Christianity is shrinking by about 20,000. The difference between +20,000 and -20,000 is actually 40,000, and this speed difference will greatly shrink the % Christian in the country. The cause: the conversion rate in Turkey is greatly outstripped by the number of Turkish believers who defect or immigrate.
3. Pop+/C+/C greater. In 12 countries, both population and Christianity are growing, but Christianity is growing faster. Zambia is the largest example: its population is adding a net of 549,000 yearly, while its Christian population is adding a net of 552,000 yearly. This is a very slim lead, but it always leads to an increase in % Christian.
4. Pop-/C+/C greater. In 5 countries, the population is shrinking but Christianity is growing. The largest example is Belarus, where the population is shrinking by -17,000 yearly, but Christianity is growing by +42,000. This will lead to a significant increase in % Christian. Since Belarus is already largely Christian (Orthodox), it means the high % Christian will be stable and grow. Likely some mix of conversion and immigration is causing this.
5. Pop-/C-/C Greater. In 14 countries, both the population and Christianity are suffering net losses, but Christianity's loss is less. Russia is the largest example: the population is shrinking by -128,000 per year, and Christianity by about -100,000 per year. Some mix of deaths, conversions and immigrations is at play. the result: in most instances, the country's % Christian will grow.
6. Pop-/C-/P Greater. In 13 countries, a similar situation--population and Christianity are suffering net losses, but Christianity's loss is greater. Italy is the largest example. It's losing 88,000 per year from its population, while Christianity is losing -222,000 per year. Obviously, there is a significant loss to defection. In these scenarios, % Christian always declines by a significant amount.
Understanding the exact scenario of growth, and the reasons for it, can inform strategy. In scenario 1, for example, there is growth in Christianity--it's just not fast enough. That's an issue of scale. In scenario 5, there is also growth, but it's being impacted by other factors (aging, death, immigration, demographic crash, etc). One shouldn't assume that just because the church is growing that the strategy is appropriate; nor should we assume that just because the church is shrinking, the current strategies are wrong.