Final answer:
The Whitman Massacre and subsequent Cayuse War were triggered by a measles outbreak that decimated about half of the local Cayuse population, ultimately leading to conflicts and the loss of Native American lives and land.
Step-by-step explanation:
The Whitman Massacre and subsequent Cayuse War occurred after d. a measles outbreak killed about half the local Cayuse. This tragic event unfolded when missionaries Dr. Marcus Whitman and his wife Narcissa, who had settled in the Cayuse territory, attempted to convert the Cayuse people to Christianity. The introduction of new diseases like measles by white settlers took a heavy toll on the Native American population, which lacked immunity to such illnesses. The Cayuse suffered devastating losses, and in their grief and desperation, some members of the Cayuse tribe murdered the Whitmans and several other settlers in 1847. This event triggered the Cayuse War as the United States settlers and government forces sought retribution, leading to years of conflict and further loss of life and land for the Cayuse people.