Actually, the treaties are NOT being violated anymore, but are being enforced to the letter by the tribes, which demand all of the goodies and money that Uncle Sam promised them when those treaties were first negotiated.
The tribes have become quite sophisticated legally, with some real aggressive tribal lawyers, courtesy of the 1975 Indian Education and Self-determination Act, which sent them through law school on Uncle Sam's dime.
Land ownership in the tribes, like everything else, is complicated. Typically, the land is owned by the tribe as a whole, and individual properties are parceled out and regulated by the tribal councils. How this is done is different from tribe to tribe, and can be quite corrupt. As the old adage goes, the tribe can give and the tribe can take away, based on who you know and who you have pissed off.
Concerning whether or not individual Indians can leave the reservation and maintain their homes and status, again it is complicated and varies from tribe to tribe. BUT, generally speaking, if an Indian leaves the reservation and takes up work and a residence outside of the tribe, then he or she loses all federal benefits and direct services, including health care, arising from the treaty governing the respective reservation. This caused a big problem during the 1950s Indian relocation program, where large masses of Indians were in fact encouraged to move to the cities and work and live there by the federal government. Those that took up the offer were given a single one-way bus ticket to a designated city and set-up with an apartment, and then turned completely loose, without any of their former services provided by the government. More often than not, the urbanized Indians failed, and reverted back into poverty and alcoholism.
Needless to say, the incentives to leave the reservation for greener pastures collapsed on the failure of urban relocation, and that's why most reservation Indians are wholly content to remain where they are and get what federal direct services they can from their treaties.
Thank you for a great answer. The only tribes we have in New England are for casinos. This is a very “western” issue that we hear little about.