This topic is generating a high number of very poor quality responses that do nothing except repeat often offensive stereotypes about residents of the Southern United States. If you can not answer the question to the standards expected here, please refrain from responding.
hi! fyi, you can get started on this recent post
The South wasn't always the "most religious" part of the United States. At first, there was nothing like our modern legal concept of freedom of religion anywhere in the original colonies; North and South alike persecuted minority religions and sometimes failed to tolerate fellow Protestant Christians outside their own state church denominations. There were some exceptions, like the former Dutch colony of New York and the Quaker colony of Pennsylvania, where religious minorities were afforded more protection--but only by comparison.
Even after the Revolution, the Bill of Rights initially applied only to the federal government. At the state level, late-18th-century Virginia and Kentucky, where "blasphemy" was decriminalized, arguably enjoyed more religious freedom than New England. However, by the mid-19th century, immigration patterns had produced a contiguous bloc of Protestants in the Southern states (except for Louisiana, about which more in a minute), while the North had become roughly one-quarter Catholic. The legal battles slowly won by Catholics, Jews, and Quakers during this period began to give religious plurality a toehold in the North.
In the South, however, Confederate ideology had begun to take root starting in the 1830s. The Confederates believed that democracy was a failed experiment, and should be replaced by a hereditary aristocracy in the mold of 18th-century Britain (that is, before the Napoleonic Wars and mass conscription required the grudging extension of voting rights to commoners). Critically, to make the idea of a permanent "Norman" aristocracy appealing to white Southern elites who were, just like in the North, not wholly British but a mix of European ethnicities, the Confederates began to promote the idea of a single Southern "white race"--defined by skin color and Protestant religion rather than national origin or a specific religious denomination.
The Confederate South began to separate into two halves, roughly equal in population: the peripheral areas that interfaced with the capitalist North and Europe via rivers, ports, and border towns, and the closed, fortified feudal domains of the interior. There, a lord's serfs were expected to adopt his religion, and his slaves were forced to do so. This meant that there was literally no place for non-Protestants to exist socially in the interior--only in the border zones, where outsiders were depended upon to facilitate trade. Catholic Louisiana, which had become a state in 1812, was the exception that proves the rule--the biggest border zone of all. The South as a whole supplied 75% of the world's cotton in the mid-19th century, and most of that left from the port of New Orleans.
Nationwide legal religious freedom was only finally established in the aftermath of the Civil War, via the 14th Amendment in 1868. This was perceived by the defeated Confederate lords as a direct assault on their political power, and they were correct in their assessment. By creating universal citizenship and obligating the states to protect the rights of all American citizens, author John Bingham was very intentionally eliminating the legal basis of a feudal aristocracy. The resentments this created in the interior zones of the former Confederacy linger to this day.
Sources: River of Dark Dreams, Walter Johnson; Slavery as a Cause of the Civil War, ed. Edwin Rozwenc; Normans and Saxons, Ritchie Devon Watson Jr.; Please Don't Wish Me a Merry Christmas, Stephen Feldman; I grew up in West Virginia.
Maybe a better question would be: why is the South still feeling the effects of the Second Great Awakening while the North has seems to move away from it?
There are a ton of great reasons for this outside of cultural evolution. The base protestant influences in the different regions show a lot more why the south ended up more culturally religious. There are very conservative religious blocks on the west coast (and a fair amount in the midwest as well).
Here is a MAP for reference. This is the current picture of denomination breakdown in the US but is a pretty good picture of historical influence as well.
The southern baptist convention is one of the major religious influencers historically in the south. They tend to be heavily conservative and involved in politics. There is a cultural aspect to their historical theology. To sum up it would be something like Our job on earth is to bring about a more righteous world through our actions, speech, and politics in the name of God. Evangelicalism took hold very strongly in this denomination.
The west coast is tricky. It is a hotbed of conservatism and evangelicalism. BUT there are huge population centers that curb a fair amount of that. And the very far coast (actually land touching water) has had some strong movements that are anti-evangelical. From the early hippy movement, to the gay rights movement. But interior west Coast is very conservative. And there are some current very large conservative evangelical churches on the west coast. Showing that the area is still highly religious.
The NE has more of a liberal denominational influence that tends to be less culturally religious. BUT the area is still highly religious just not the conservative evangelical style that we see so much of.
