It was generated by the peculiar position Native Americans stood at with regard to the land they inhabited as opposed to any other people living in America. While everyone else arrived to America from someplace else, and so the times and ways they became US citizens depended on the time they and their ancestors had spent in the US, Native Americans were all born in America as were their ancestors. They had actually been there before the United States of American even existed.
There was never a question whether or not Native Americans were subject to the US laws: they were. Theirs citizenship, though, was a separate and distinct question. Apparently.
A first attempt at handling the issue appears in the treaty of 1778 between the United States and the Lenni Lenape tribe. It was envisioned here that the different Indian nations could be admitted to the United States the same way other states were. But this solution presented implicit issues the US Government didn’t seem keen to address and was soon abandoned.
In 1868, following the Civil War, the US Government passed the Fourteenth Amendment, which stated that “all persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.” It would sound as all Indians were automatically entitled to the US citizenship since they certainly met the requirements.
Throughout all this time, while Native Americans as a social group remained in a limbo, individuals could gain citizenship for different reasons. One such reason was the General Allotment Act (best known as the Dawes Act), which was passed in 1887.
This act destroyed the traditional Indian practice to take care of the land communally, chopped up reservations in little lots and assigned a lot to every single family, appropriating all the land that was left after the allotment. If after twenty years the head of the family had proven himself a competent farmer, he could become owner of that allotment. Citizenship was attached to the allotment, although there was much argument whether the person acquired US citizenship upon accepting the allotment or upon proving himself a competent farmer twenty years after accepting said allotment.
Much argument was further arisen by the participation of many Native Americans to WWI in spite of not being citizens of the US. It was finally in 1924 that the Congress passed the Indian Citizenship Act that granted US citizenship to all Native Americans born in the United States.
Native American Netroots – American Indian Citizenship