So where white people who live in south region of the USA did come from? For example there are a lot of Americans with german ancestry in midwest, english americans(WASPs) in northeast. But what is the origin of white people in the south region?
There are many mixed race people in the south region of the USA so some white people have some degree of nonwhite ancestry, including some white people partially descended from Indians living there before 1492.
For example, one of my nephews is said to have had a Cherokee great great grandmother, though his father suspected that she might actually have been black and the family might have only claimed that she was Indian.
Before the Civil Rights Movement the southern states had tyrannical state governments that restricted civil rights to white people. And most states used the one drop of blood rule to determine race. And no, it wasn't a rule that one drop of superior white blood made someone white, but a rule that one drop of inferior black blood made someone 100 percent black in the eyes of the law. So if someone had even one known black ancestor, no matter how many centuries earlier, they were considered black and denied civil rights.
So many people who were slightly darker than most white people claimed that they were part Indian instead of part black to avoid the oppression of black people. And some southern states worried about the "problem" of people escaping oppression by claiming to be part Indian instead of part black, and so enacted laws making Indians legally black, and so claiming Indian ancestors became identical to claiming black ancestors. But the state of Virginia had to limit the oppression of people with Indian ancestors to those with Indian great great grandparents or more recent, in order not to affect the First Families of Virginia who could trace their ancestry to Pocahontas (c. 1596-1917).
Due to mixed race relationships, there are many white people in the South who have some Indian ancestors whose people have lived there since before Columbus.
The first white settlers in the American south were Spanish in Florida. The first white child in the future USA was born in San Augustine, Florida in about 1566.
France claimed the entire Mississippi River drainage basin as the Louisiana Territory in 1678. The earliest French settlements were in what is now Illinois. New Orleans was founded in 1718.
When Britain conquered French Canada in the Seven Years War, France ceded the Louisiana Territory west of the Mississippi to Spain and the Louisiana Territory east of the Mississippi River to Great Britain. Saint Louis, Missouri was founded in 1764.
So the early settlers of the Mississippi River Basin were French and Spanish.
Back in the 17th century (1601-1700) several European colonies were established on the eastern seacoast.
French Canada was founded in 1604-08. The English Virginia colony was founded in 1608 at Jamestown. The Dutch New Netherland colony founded Albany in 1617 and New York in 1626. The English Pilgrims founded the Plymouth colony in 1620. The English Maryland colony was founded in 1634. The Swedish colony of New Sweden was founded on both banks of the Delaware River in New Jersey, Pennsylvania, and Delaware in 1638.
By about 1630 there were probably a few hundred Europeans living in each of several colonies in northern North America: 1) Spanish New Mexico, 2) French Louisiana Territory, 3) Spanish Florida, 4) French Canada, 5 English Virginia, 6) English Plymouth, 7) English Maryland, 8) Dutch and members of other ethic groups in New Netherland. Possibly fewer than 5,000 total Europeans north of the present Mexican border.
The Massachusetts Bay Colony was founded in 1628/29 by English Puritans and about 20,000 English Puritans emigrated to Massachusetts Bay in 1630-1640, multiplying the European population north of Mexico several times. A number of other English colonies were founded in the later 17th century and the 18th century.
Most of the English colonies were settled by people from Britain - English, Scottish, Welsh, and Irish - and most were Protestants since most colonies required settlers to be Protestants. New Netherland, Maryland, and Pennsylvania had religious tolerance.
Pennsylvania was probably the first English colony to have many non British settlers, attracting many Germans.
Britain conquered the Acadia region, the Maritime Provinces of modern Canada, in 1710, and in 1763 the French Acadians were ordered to leave. Most ended up in Louisiana, now a Spanish territory, and became the ancestors of the Cajuns.
In the Virginia Colony:
England supplied the great majority of colonists. In 1608, the first Poles and Slovaks arrived as part of a group of skilled craftsmen. In 1619, the first Africans arrived, though the concept of racially based slavery did not evolve for several decades. In the mid-17th century, French Huguenots arrived in the colony. In the early 18th century, German specialists arrived to establish the Germanna settlement. Scots and Scots-Irish settled on the Virginia frontier. Some Welsh arrived including the ancestors of Thomas Jefferson.
During the 17th century Northern Ireland was also being colonized, mostly by Protestant Scots. And many of those Scotch-Irish later emigrated to the British colonies in North America.
From 1717 to the next thirty or so years, the primary points of entry for the Ulster immigrants were Philadelphia, Pennsylvania, and New Castle, Delaware. The Scotch-Irish radiated westward across the Alleghenies, as well as into Virginia, North Carolina, South Carolina, Georgia, Kentucky, and Tennessee. The typical migration involved small networks of related families who settled together, worshipped together, and intermarried, avoiding outsiders.
So scotch-Irish became a significant fraction of the population of the USA including the southern States.
Men who were members of the Confederate Army in 1861-1865 should be southern enough to count as southerners by most definitions.
Compared to the U.S. Army at the time, the Confederate army was not very ethnically diverse. Ninety-one percent of Confederate soldiers were native-born white men and only 9% were foreign-born white men, Irishmen being the largest group with others including Germans, French, Mexicans, and British. A small number of Asian men were forcibly inducted into the Confederate army against their will when they arrived in Louisiana from overseas.
I expect that the places of origin of the ancestors of the 91 percent of southern soldiers who were native born would be similar to those of the Rebels who were foreign born. Mostly Ireland, Germany, France, Mexico, and Britain, with smaller numbers from other mostly European countries. But in each generation the proportions of immigrants from different countries would vary a bit.
In the 20th century a number of factors changed the composition of the southern population.
There was the Great migration (African-American) of 6,000,000 African-Americans from the rural south to the urban Northeast, Midwest, and West between 1910 and 1970. The success of the Civil Rights movement lead to a smaller New Great Migration of African-Americans back to the South since 1965.
Beginning in World war II (1941-1945) the southern states began to be industrialized, which of course attracted many workers from other parts of the USA to work in the factories.
For example, a great grandfather of mine from Pennsylvania worked as a "water boy" in a factory in Texas City, Texas during World War II, despite being in his 70s during the war.
Also during the 20th century air conditioning became more and more common in public buildings and homes, thus encouraging people from the north to move to the south despite the heat.
And so for decades retired people from all over the USA have moved to different states to retire to, with Florida and Arizona being the most common destinations. With air conditioning, the retirees don't have to fear death from the heat so much.
in 2018 the states with the largest numbers of retirees moving in were Florida, Arizona, North Carolina, South Carolina, Nevada, Texas, Oregon, Idaho, Alabama, and Georgia, and Florida was clearly in the lead.
Large numbers of Hispanics or Latinos have emigrated to the USA, including the south, since 1965, and a significant proportion of Hispanics would be classified as more or less white people by most persons. Thus a significant proportion of the white people in the south are comparatively recent Hispanic immigrants.
And this is just a brief summary of some of the main aspects of the ancestry of "US south region white people" that have occurred to me.