As the English, French, and Spanish explorers came to North America, they brought tremendous changes to American Indian tribes. ... Diseases such as smallpox, influenza, measles, and even chicken pox proved deadly to American Indians. Europeans were used to these diseases, but Indian people had no resistance to them.
Adding on to the previous answer, they also massacred the indigenous people in the name of religion and to claim the land. They also enslaved them in places like the Caribbean, where they were used to farm sugar cane and other cash crops. Colonists sent by European countries later on had a hard time adapting the the unfamiliar climates and lack of food, and were often unskilled at surviving.
