Other than that obvious flaw in semantics and actuality of the diction at hand, why do certain historians disagree? There are many books written about this. For example, one title of a book is called "They Came Before Columbus." Even the Vikings touched base in or around Newfoundland during the year 1000 A.D or thereabouts. I have read before that many humanoids reached the continent of America way before Columbus albeit things were not always documented very well, during those times. It has also been said that people from Asia reached America thousands of years before Columbus and in the book mentioned above, the guy claims that an African discovery of America happened before Christopher Columbus.
I really don't know who discovered America first, but since there were already people dwelling at the place who were partying like a rock star (while wearing paint and feathers), I can honestly say that Christopher Columbus was not the first. Ha!
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---End of Post "How did Christopher Columbus discover America?"