The Creek War (1813-14) was a brutal civil conflict that had a profound effect on the Seminole nation. In 1813, traditionalist Creeks known as Red Sticks took up arms against Coweta Creeks, who were assimilating with the dominant white culture. The assimilationists quickly allied with the United States and General Andrew Jackson. Under Jackson, the pro-U.S. Creeks crushed the Red Sticks in the famous battle of Horseshoe Bend (1814), where they killed 800 warriors. (For Americans, this avenged the 1813 attack on Fort Mims, where Red Sticks killed 500 white soldiers and settlers.)
The overall devastation of the Creek War had a lasting effect on Osceola's people. Red Stick refugees -- Osceola and his mother among them -- fled south to Florida, where they joined the Seminoles. In Florida, the Red Sticks, who were also known as Mikasukis, became the leading militants within the Seminole confederacy.
Mahon 6, Sprague Origin 100-1, Wickman xx-xxi, Carter 23: 453.
Part 2, War: l