Conversation so far:
What war was Osceola leading?
In 1836, Osceola led a small group of warriors in the Seminole resistance during the Second Seminole War.
What attacks caused the Second Seminole War?
The Dade massacre was an 1835 defeat for the United States Army that greatly escalated the Second Seminole War, which lasted until 1842.

Question: Why did they kill him?
Self-contained rewrite: Why did the Seminoles kill Wiley Thompson?