Three Timelines

(i) In our timeline:

Alexander the Great died in 323 BCE;
John Rolfe married Pocohontas in 1614;
Pocohontas died in 1617;
Rolfe was killed in 1622;
the Rolfe name died out;
however, through their granddaughter, Rolfe and Pocohontas became ancestors of prominent Virginian families;
Poul Anderson, Harry Turtledove, SM Stirling etc wrote sf;
Stirling wrote Conquistador.

(ii) In the FirstSide timeline:

Alexander died in 323 BCE;
John Rolfe married Pocohontas in 1614;
both were killed in 1622;
but Pocohontas had borne two more sons, including John II, thus starting the Virginian Rolfe lineage;
in 1946, John Rolfe VI discovered the Gate;
Anderson, Turtledove etc wrote sf.

(iii) In the Commonwealth of New Virginia timeline:

Alexander died in 280 BCE;
Europeans did not invade North America;
John Rolfe VI arrived through the Gate and founded the Commonwealth.