The largest Christian nation on earth is the United States

Many people don't realize this here on earth unless they live in the U.S. and sometimes not even then. So, secular Christianity including Christmas is the strongest among this most populated Country of Christians. Europe consists mostly of Christian Secular ruled nations too and Russia is a Russian orthodox Christian nation there too along with all of North and South America. So, the most populated continent of Christians would likely be North and South America too.

The influx of Islamic refugees over time could change the population percentages of Europe over time. So, all the wars between Christians and Muslims over Europe the last 1000 years might become moot because Muslims have more children than Christians generally speaking, at least in Europe. In North and South America people who live south of the U.S. border tend to have more children and tend to be Christian as well. So, in North and South America the numbers of Christians is growing rapidly.

However, it is hard to say what is going to happen now to Europe because of the refugee crisis because there is not the will to prevent Russia from making the refugee crisis now even worse than it is now by the Actions of the Russian Army in Syria. So, at least for Europe it is very important what Russia is going to do now. Because it will mean whether millions of refugees head towards Europe or 10s of millions of refugees now head towards Europe during the next 5 to 10 years.