By the time Europeans sought to conquer the New World, the diseases they brought at first contact in the late 15th century and onward had already spread ahead of them and killed off a significant portion of the indigenous inhabitants. Is there any evidence of something similar happening in the 9th-10th century when Norse explorers reached Canada? There is evidence of interactions with Indigenous Americans at the time, which would presumably allow for the spreading of germs that cause a similar spread of disease. Did this happen? If not, why not?
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