Because Keith, McClure and Arnett are all names of Scotch-Irish origin, I have assumed all three families came from there early in American history. History tells us during the years 1768-1775 many emigrants from the British Isles, mostly of Scotch-Irish descent married Cherokee women and generated mixed blood families of importance to the nation. Regardless, because of American law the descendents remained unequivocally Cherokee. They did not have citizenship rights, in fact they did not get U.S. citizenship rights until October 1901. Many of these Cherokees adopted Scotch and Irish names.
Ruben William Freeman Keith said, his father and four brothers came to America from Northern Scotland "as slaves." It was most likely his great grandfather or an earlier generation that came to America. They may have been indentured servants and considered themselves slaves. In fact they were slaves for the indenture period, they could be brought or sold along with their indenture contract.
A recent study published by Western Carolina University "From Ulster To Carolina" traces many Scotch-Irish families in America. It is probable the Keith, the Arnett and the McClure families followed a similar route. In all, some 250,000 people left Ulster for America in the period from 1718-1800. It has been estimated 20,000 were Anglo-Irish, 20,000 were Gaelic-Irish and the remainder Scotch-Irish as they came to be called in America.
Agents hired by ship owners, American land speculators, and those seeking to profit from indentured labor, scoured the Irish and Scot countryside promoting prospects for a poor man in America. The majority of the migrants were Presbyterians, too poor to afford passage and had to contract as indentured servants. A few migrants came directly to Charleston or Savanna, most however landed in Philadelphia, worked in southeastern Pennsylvania to discharge their indenture, then migrated west or south through Maryland, Virginia, North Carolina, South Carolina and Georgia.