The highest reported share of self-described atheists is in China: an astounding 47 percent. Faith has a complicated history in China. The state is deeply skeptical of organized religion, which it has long considered a threat to its authority.
In the Taiping rebellion of the 19th century, a religious cult started a Chinese civil war that killed millions of people and left the country exposed to European powers. The official ideology of the Communist government scorned both "new" Western religions and more traditionally Chinese faiths, destroying countless temples and relics during the Cultural Revolution of 1967 to 1977. While today's Chinese leaders do not seem to share Mao Zedong's fervent belief that China's rich religious history was holding it back from modernity, nor do they seem prepared to bring that history back.
Japan, where 31 percent call themselves atheist, is a little more complicated. While superficial religious observation is common – many weddings take place in churches – formal religious practice has never really recovered from the imperial era that culminated with World War Two.
For much of the 1920 through 1940s, Japan's imperial government combined an extreme form of race-based nationalism with emperor-worship and traditional Shinto practice. Some symbols of that era still remain, such as the Yasukuni shrine, though they are deeply controversial and often associated with the country's wartime abuses.
Like nationalism in Germany, a bit of a post-war taboo has developed around religion in Japan. Separately, there is an alarming trend in Japan of forced religious de-conversion, in which families may "kidnap" a loved one who as adopted a faith seen as too extreme, such as Jehovah's Witnesses, and pressure them to give it up.
One of the most surprising datapoints here might be Saudi Arabia, where 5 percent say they're atheist. Not a high number, to be sure, but higher than in many other countries, despite the extremely sensitive taboo against atheism in Saudi Arabia, which is also considered a serious crime. (In both Iraq and Afghanistan, for instance, less than 1 percent of respondents called themselves atheists.) We looked earlier at the surprisingly robust community of underground Saudi atheists.
In addition to Iraq and Afghanistan, religious sentiment is strong in Ghana, Nigeria, Armenia and Fiji, where more than nine in 10 people say they're religious. WIN/Gallup notes that religiosity is highest among the poor and, to a lesser extent, among the less educated, which certainly correlates among the most religious countries. (Ghana's GDP per capita, for instance, ranks 173rd worldwide.)
As for Italy, a stone's throw from the Vatican chapel where Pope Francis spoke on Wednesday, the Catholic Church has little to fear. Despite a gradual slide in Catholic baptisms in Italy over the past several decades, nearly three-fourths of Italians consider themselves religious. That number has actually grown one percent since 2005, according to WIN/Gallup, bucking the trend toward weaker religious feeling seen elsewhere in the world.