Which of the following agreements caused the native american tribes to lose two thirds of the southern portion of ohio

The correct answer should be Treaty of Greenville

It was a treaty that ended the battle of Fallen Timbers and ended the Northwest Indian War. Although the British supported the Natives and the Natives refused to leave their  territory, they had to eventually since the American troops made a decisive victory and the Native Americans did not have a choice. This was responsible for the loss of numerous lives.