It does seem that the P-40 was generally used more successfully by its home nation (USA) than the P-39 was.

True, But it’s war-saving service was more in Commonwealth use.

Anyone ever read much on the P-40 as opposed to the P-39 in U.S. service. What was it about the Warhawk series that seemingly made it so much more prevalent than the Airacobra?

The P-40 was avaliable for export sales prior to the US entry to W.W.II. – In part built for foreign sales.

The P-39 wasn’t quite as good as the P-40; IMHO, the difference, as stated before, being small, but on either side of the gulf between ‘adequate’ and ‘inadequate’.

The other difference was that the P-39 was a more complex aircraft systems wise, requiring more maintenance, and I think more support equipment, while the P-40 was a more robust and lower tech – better for secondary theatres like the Middle and Far East where conditions were tough and make-do a requirement.

Very general, but broadly correct, I think.