Eklund, Gordon. "Red Skins"
Divergence: 1219 CE
What if: The Americas were discovered in 1219 by a Muslim, but not seriously colonized until Europeans showed up c. 1700.
Summary: 100 years after AmerInds banded together to handle the immigration problem, Nazi Germany threatens war if scientist-refugees are not returned.
Published: In The Magazine of Fantasy and Science Fiction, January 1981.