The following is taken from Encyclopedia Britannica on-line.

World War I broke Europe’s waning self-confidence in the merits of its own civilization and, because it was fought between Christian nations, weakened worldwide Christianity. The seizure of power by a formally atheist government in Russia in 1917 brought negative pressure on Christendom and sharpened the social and working class conflicts of western Europe and the United States. During the following 40 years the Protestant churches in Europe suffered inestimable losses in adherents and formal influence.