First Contact

Before it was a Star Trek Movie, it was a SF novella. I think there were dozens of SF stories about being the first to encounter alien civilisations, and the problems that might ensue.

In 1400 AD, (and much earlier) Europeans were sailing up and down the Atlantic, and the Chinese were sailing back and forth across the Indian Ocean. A New World Population of up to 100,000,000, mostly from Mexico to Peru, had been isolated from all Eurasian diseases for at least 12,000 years, and in most cases, more like 18,000 years.  Making alcoholic beverages had first occurred in Asia thousands of years after the split, so the genes which discouraged overconsumption - things which made you have a headache or a hangover - had never developed in the Native American populations either.

It was a poised, unstable situation. With that much separation, and technology advancing enough that longer-distance sailing was possible, the massive death of tens of millions of New World natives was inevitable, and the defenses they had never developed against alcohol overcomsumption made their contact with Europeans unbalanced right out of the gate.

This did not make land-stealing, slavery, or violence inevitable.  But a great deal of misery was lying out there on the counter, just waiting to happen once first contact occurred.