There's multiple reasons for the lack of unity between the Indian tribes against the European invasion and expansion on their territory. The Indians were divided into multiple groups, some of which had already had problems and bad blood between them, so alliances between tribes like that were not the first choice in mind. Also, the Europeans played well tactically, by promising some of the tribes certain things if they ally with them, so once the Europeans managed to get what they wanted they were turning against their Indian allies who were pretty much isolated bu that point because of their actions. The conquering of new territories by the Europeans also was very big factor, because they managed to cut the connections between the tribes, thus not allowing them to be able to create alliances and be united against them.
The correct answer is C) establishment of the Freedmen's Bureau.
The acts by Congress that were intended to prevent this repressive social and political order were the establishment of the Freedmen's Bureau.
In a time of ecom¿nomic problems and political instability, the Freedmen's Bureau was a real help for former black slaves and poor white people that lived in the south and practically had nothing after the conclusion of the American Civil War.
The US Congress approved the establishment of the Freedmen's Bureau in 1865 to assist these people with medical attention, food, shelter, and education. Unfortunately, there was not enough money to accomplish these, besides the political "climate" in the racist's southern states never accepted this Freedmen's Bureau.
To provide a governing framework if im correct but please add a little more information
