Generally, people in rich countries think people can be moral without believing in God.

Source

I quote from the report published by the Pew Research Center:

Many people around the world think it is necessary to believe in God to be a moral person, according to surveys in 39 countries by the Pew Research Center. However, this view is more common in poorer countries than in wealthier ones........ 

The U.S., however, stands out as a clear exception to this pattern. Americans are much more likely than their economic counterparts to say belief in God is essential to morality.

So what accounts for the differences in developed countries?

There are also significant divides within some countries based on age and education, particularly in Europe and North America. In general, individuals age 50 or older and those without a college education are more likely to link morality to religion. For example, in Greece, 62% of older adults say it is necessary to believe in God to be a moral person, while just 29% of 18- to 29-year-olds agree. In the U.S., a majority of individuals without a college degree (59%) say faith is essential to be an upright person, while fewer than four-in-ten college graduates say the same (37%).

I offer the hypothesis that the U.S. is such an outlier among affluent countries. This is a country that has had a history of religious diversity, and since the founding of the USA there has been a separation of state and church. Thus churches have had to compete for members, churchgoers, and resources. They have successfully done so, so that there are more people in the USA who say that religion is important in their daily lives than in other affluent countries. I would suppose that people who so respond are more likely to feel that religion is the basis of morality.