What was the greatest effect of European exploration on decrease in native American population?

The greatest effect of European exploration on the decrease in Native American populations was the introduction of diseases such as smallpox, influenza, and measles, to which Indigenous peoples had no immunity. This led to devastating epidemics that wiped out large portions of Native populations. Additionally, violent conflicts and displacement due to European colonization further contributed to the dramatic decline in their numbers. Together, these factors resulted in a significant and tragic loss of life and culture among Native American communities.