Final answer:
Christopher Columbus unintentionally caused a massive decline in Native American populations due to diseases like smallpox, and initiated a period of European colonization that led to the oppression and genocide of indigenous cultures.
Step-by-step explanation:
What Christopher Columbus unintentionally did to Native American cultures was instigate a disastrous decline in their populations and a catastrophic impact on their ways of life. When Columbus arrived in the Americas, he brought with him a host of Eurasian diseases, such as smallpox, which the native populations had no immunity against.
This led to one of the most abrupt and severe population disasters in human history, where an estimated 90% of the indigenous population was wiped out.
For example, the Caribbean island of Hispaniola had over a million inhabitants before Columbus's arrival; 50 years later, only 500 natives remained. Furthermore, Columbus's expeditions began a cycle of violence, oppression, and genocide against Native American cultures, and set the stage for centuries of European colonization and exploitation of the New World.