B. The treaty was signed by a small group that did not represent the tribe.
Explanation:
The Treaty of Fort Gibson basically enable US government to take over the Seminole's Territory. In exchange, the government promise to provide assistance on Seminole's reallocation process.
This treaty has more downsides than benefits for the Seminole people.
At that time, the treaty was signed only by 3 Representatives of the Seminole tribe. They did it without obtaining the consent of the majority members of the tribes that have to experience the negative impact of the treaty. This is why they argued that the treaty was illegitimate and unenforceable.
