Answer:
Smallpox virus
Step-by-step explanation:
At that time , Small pox virus was not something that you can stumbled upon North American region. But, it is pretty common In Europe (Where the settlers came from).
When the settlers came to north America, a lot of them acted as carriers for this virus. They spread it to Native American community during contact. Since Native Americans haven't developed immunity for this virus, this illnesses caused a lot of death within Native American community,.