When Aaron Köhler tries to talk to people in Cottbus, Germany, about Jesus, church, and faith, he can’t assume they know what he’s talking about. Many in the city near the Polish border don’t know anything about Christianity. Köhler has had people ask him whether Christmas and Easter are Christian holidays, and if so, what they’re about. One time, he talked to someone at a local market who wasn’t familiar with the name Jesus. The person had never even heard it, that they could recall.

“That was crazy for me. In the ‘land of the Reformation,’ in a supposedly ‘Christian country,’ these people don’t even know the basic basics,” said Köhler, who co-pastors a church plant.

According to the most recent data, more than 60 percent of Germans identify as Christian. A little more than a quarter say they have no religion. Zoom in a little closer, though, and stark regional differences emerge. In the western part of the country—which includes Hamburg, Munich, Cologne, and Frankfurt—three-quarters of the population identify as Christian. But in the east, the region that was a Soviet Union satellite state from 1949 to 1990, only a quarter of Germans are Christian, with nearly 70 percent identifying themselves as “nonbelievers.”

Christianity is declining in much of formerly Protestant Europe. But eastern Germany stands out, even compared with other rapidly secularizing nations. Here, large swaths of the population have had no serious contact with Christianity for three generations. Köhler said, “For decades, there was no prayer, no Bible at home, no church attendance. After all these years, people don’t know what they don’t know.”

The regional differences are easily traced to the division of the country after its defeat in World War II. The French, British, and American-controlled sectors in the west merged into the German Federal Republic in 1949. The Soviet-controlled East formed the German Democratic Republic, a socialist state with totalitarian leaders who suppressed religion. The Christian population in East Germany fell from about 90 percent in 1949 to only 30 percent in 1990.