European colonization and exploration resulted in the deaths of millions of people.
For example, when European countries like Spain, France, and England started to colonize the North American continent, they encountered new groups of people they never met before. These groups included a wide range of American Indian tribes. When interacting with these tribes, Europeans spread diseases to these American Indians that they did not have immunity to (such as whooping cough and malaria). This resulted in the decimation of the American Indian population.
Along with this, many Europeans died in this process. This was caused by many different factors including living conditions, exposure to new diseases/elements, etc.