Identify three reasons that may explain the distribution of Indigenous Americans
in the US.

The ancestors of living Native Americans arrived in what is now the United States at least 15,000 years ago, possibly much earlier, from Asia via Beringia.[3] A vast variety of peoples, societies and cultures subsequently developed. European colonization of the Americas, which began in 1492, resulted in a precipitous decline in Native American population through introduced diseases, warfare, ethnic cleansing, and slavery.[4][5][6][7] After its formation, the United States, as part of its policy of settler colonialism, continued to wage war and perpetrated massacres[8] against many Native American peoples, removed them from their ancestral lands, and subjected them to one-sided treaties and to discriminatory government policies, later focused on forced assimilation, into the 20th century. Since the 1960s, Native American self-determination movements have resulted in changes to the lives of Native Americans, though there are still many contemporary issues faced by Native Americans. Today, there are over five million Native Americans in the United States, 78% of whom live outside reservations: California, Arizona and Oklahoma have the largest populations of Native Americans in the United States. Most Native Americans live in rural areas or small-town areas.

When the United States was created, established Native American tribes were generally considered semi-independent nations, as they generally lived in communities separate from white settlers. The federal government signed treaties at a government-to-government level until the Indian Appropriations Act of 1871 ended recognition of independent native nations, and started treating them as "domestic dependent nations" subject to federal law. This law did preserve the rights and privileges agreed to under the treaties, including a large degree of tribal sovereignty. For this reason, many (but not all) Native American reservations are still independent of state law and actions of tribal citizens on these reservations are subject only to tribal courts and federal law.

The Indian Citizenship Act of 1924 granted U.S. citizenship to all Native Americans born in the United States who had not yet obtained it. This emptied the "Indians not taxed" category established by the United States Constitution, allowed natives to vote in state and federal elections, and extended the Fourteenth Amendment protections granted to people "subject to the jurisdiction" of the United States. However, some states continued to deny Native Americans voting rights for several decades. Bill of Rights protections do not apply to tribal governments, except for those mandated by the Indian Civil Rights Act of 1968.