The world's religious landscape has changed dramatically over the past 100 years. Thanks to migration, people from various faiths today are living in increasingly closer proximity. In fact, most countries have become more diverse when it comes to the religious background of their inhabitants.
Of course, adherents of the same faith can find themselves living in countries with very different levels of religious diversity. Muslims in Somalia, for instance, live in a far more religiously homogenous country than Muslims in Sweden. Religious diversity can have a profound impact on how people interact with each other politically, culturally, and socially. Diversity of faiths can also influence the role of religion in conflict.
This subject is covered in depth in the Yearbook of International Religious Demography, published in July 2015, which introduces the Religious Diversity Index (RDI). The index describes the inter-religious diversity of a particular country or region's population using a scale from 0.00 (no diversity) to 1.00 (greatest possible diversity).
Of the ten countries with the highest RDI values in 2010, the top six were in Asia (South Korea, China, Singapore, Taiwan, Hong Kong, Vietnam), the seventh in South America (Suriname), and the remaining three in Africa (Mauritius, Cote d'Ivoire, Benin).
But who lives in an environment of high religious diversity? In the yearbook, we compare Christians, Muslims, and the non-religious by examining the RDI values of countries in which they lived in 1910 compared to 2010.
Christians live in contexts of greater religious diversity now than 100 years ago.
For Christians, religious diversity has increased compared to a century ago. In 1910 Christians were concentrated in Europe and the Americas, but today most live in the global South. Many live in religiously diverse countries such as China and Nigeria. In addition, back in 1910 some 95 per cent of Christians lived in countries that were more than 80 per cent Christian; by 2010, this had fallen to just above 50 per cent.
Muslims on the other hand live in less religiously diverse countries than they did in 1910. Indonesia and Pakistan are two examples of such countries. Back then, Muslims lived in countries that were more diverse than the global average, but by 2010 the opposite was true.
A century ago, fewer than 20 per cent of all Muslims lived in countries with very low RDI values. By 2010 this had increased to more than 30 per cent. Still, millions of Muslims today live as minorities in majority Hindu, Christian, and Buddhist countries, such as India, the United States, and Myanmar.
The most striking change over the 20th century has been among the non-religious. In 1910, agnostics and atheists lived in countries with little diversity. By 2010 they lived in very diverse countries, the highest of any 'religion.'
The explanation for this shift is simple. In 1910, most non-religious people lived as small minorities in majority Christian regions (Europe and Northern America), whereas in 2010 the largest contingent lived in China, the world's most religiously diverse country. Eighty per cent of all the world's non-religious lived in countries with very low diversity in 1910, but over 60 per cent in 2010 lived in countries with high diversity.
In a comparison between Christians, Muslims, and the non-religious, the overall trend is quite clear. Muslims today live in less religious diversity than in 1910, Christians live in more religious diversity, and the non-religious live in the most religiously diverse contexts.
But there are important variations for each of the religions by region. For example, Christians in Africa live in more religious diversity than either Muslims or the non-religious. But in Europe, Christians live in the least diverse environment, with Muslims and the non-religious in more religiously diverse contexts overall.
The world's population clearly lives in more religiously diversity today than a century ago, though the degree of diversity changes from place to place. Where there is more religious variety, studies have shown people are more likely to form friendships across religious and ethnic lines. Diversity affords opportunities for building mutual understanding. The complex trends outlined above can help us better understand the world's religious and non-religious populations. Crucially, they can help us understand their role in international relations, peacemaking, conflict resolution, and geopolitics.
Christians lived in more religiously diverse countries in 2010 than they did in 1910.
Ninety five per cent of all Christians lived in countries that were 80 per cent or more Christian in 1910, while in 2010, this had fallen to just over 50 per cent.
Muslims lived in less religiously diverse countries in 2010 than they did in 1910.
Fewer than 20 per cent of all Muslims lived in countries with very low religious diversity in 1910; but by 2010 this had increased to more than 30 per cent.
Non-religious people have seen the greatest change, shifting from countries less diverse than the global average in 1910, to more diverse than the average in 2010.
Eighty per cent of all the world's non-religious lived in countries with very low diversity in 1910, but over 60 per centin 2010 lived in countries with high diversity.