The easy response is to just send you to The American Indian Policy Center
Policy Center however that would be the easy way out.
Here's the condensed version on The Marshall Trilogy.
The Marshall Trilogy involved 3 cases in which Supreme Court Chief Justice Marshall presided. They were as follows:
1)Johnson v.McIntosh (1823); tribal sovereignty although impaired by European colonization cannot be dismissed. Marshall stated that 'In the establishment of these relationships [between Europeans and Indians], the rights of the original inhabitants, were in no instance, entirely disregarded. They were admitted to be the rightful occupants of the soil with legal as well as just claim to retain possession of it, and use it according to their discretion.
2)Cherokee Nation v.Georgia (1831) ruled that Indian tribes were a distinct political party separated from others, capable of managing their own affairs and governing themselves.
3)Worcester v. Georgia (1832) The court held that tribal sovereign powers were not relinquished when Indian tribes exchanged land for peace or protection.
As a result of The Marshall Trilogy, The Supreme Court both reaffirmed the sovereignty of Indian tribes and acknowledged this as predating European arrival. Because Indian nations lie within the acknowledged boundaries of The United States, Chief Justice Marshall delineated Indian tribes as 'domestic dependent nations'. It is under this definition that Indian tribes operate today.
As to what type of sovereignty Indian Nations have, that is a continued struggle and variable which changes on a regular basis. As has always been the case governments step in and see choice parcels of land and find ways to claim it as their own. The good part is that there is a much greater awareness today of the horrors which Native Americans have been forced to endure. The bad news is that there are far fewer Native Americans now than ever before and their numbers do not show signs of gain at any time in the foreseeable future.