What was responsible for killing many Indians after Europeans arrived on their land?

After Europeans arrived in the Americas, many Indigenous peoples died due to diseases such as smallpox, influenza, and measles, to which they had no immunity. These diseases spread rapidly and decimated populations. Additionally, violent conflicts and displacement caused by European colonization further contributed to the decline of Indigenous communities. The combination of disease, warfare, and disruption of their societies led to significant loss of life among Native populations.