The two American “Yankee” threads are in BS, where they belong. And no, it's not Native American.

Wiki#1 - Yankee
Dutch origin
Most linguists look to Dutch language sources, noting the extensive interaction between the Dutch colonists in New Netherland (now largely New York, New Jersey, Delaware, and western Connecticut) and the English colonists in New England (Massachusetts, Rhode Island, and eastern Connecticut).[9] The exact application, however, is uncertain; some scholars suggest that it was a term used in derision of the Dutch colonists, others that it was derisive of the English colonists.

Michael Quinion and Patrick Hanks argue that the term comes from the Dutch name Janneke, a diminutive form of Jan (John)[14] which would be Anglicized as "Yankee" due to the Dutch pronunciation of J as the English Y. Quinion and Hanks posit that it was "used as a nickname for a Dutch-speaking American in colonial times" and could have grown to include non-Dutch colonists, as well.[14] The Oxford English Dictionary calls this theory "perhaps the most plausible".

Alternatively, the Dutch given names Jan (Dutch: [j?n]) and Kees (Dutch: [ke?s]) have long been common, and the two are sometimes combined into a single name (Jan Kees). Its Anglicized spelling Yankee could, in this way, have been used to mock Dutch colonists. The chosen name Jan Kees may have been partly inspired by a dialectal rendition of Jan Kaas ("John Cheese"), the generic nickname that Southern Dutch used for Dutch people living in the North."

Wiki #2 – Yonkers:
"In July 1645, the area was granted to Adriaen van der Donck, the patroon of Colendonck. Van der Donck was known locally as the Jonkheer or Jonker (etymologically, "young gentleman", derivation of old Dutch jong (young) and heer ("lord"); in effect, "Esquire"), a word from which the name "Yonkers" is directly derived."

PS: Didja know the Germans lost the exclusive patent rights to Heroin, in the Versailles Treaty? Talk about unintended consequences!