A collection of short stories by Harry Turtledove all dealing with the same world: a timeline where the Americas were cut off from Eurasia earlier, and retained pre-Ice Age flora and fauna. Turtledove ignores the butterfly effect to preserve recognisable countries and people, and when Columbus arrives, he finds two continents with woolly mammoths, sabre-toothed tigers - and Homo erectus, referred to in-universe as “sims”, with no Homo sapiens.
Turtledove mentions that the lack of an Aztec civilisation and their gold means that Spain is considerably less well off in TTL, but he does not go into detail. His stories focus on the area corresponding to the OTL United States, which undergoes an earlier revolution in the early 1700s due to Britain taking a more absolutist turn under Stuart kings. It eventually becomes known as the Federated Commonwealths. The existence of sims as labour means black slavery is much less brutal and is abolished sooner. The question of just how human sims are, and what rights they have, is posed throughout the stories.