There are actually far more Native people today living in cities than on reservations. The 2010 US Census found that 71% of Native Americans live in urban areas, up from 67% in 2000. The cities with the highest Native populations are New York, Los Angeles, Phoenix, Oklahoma City, and Anchorage. In 2019, the city with the highest proportion of Native Americans was determined to be Tulsa, with 14% of the population identifying as Native. (It's followed by Stockton, Albuquerque, Oklahoma City, and Tucson).

In Canada, the statistics are more evenly split. In 2016, 51.8% of First Nations people lived in urban areas. The proportion of Indigenous people living on reservations varies by province, from 35.1% in Newfoundland and Labrador to 72% in Quebec. The cities with the highest populations of Indigenous people are Winnipeg, Edmonton, Vancouver, Calgary, and Toronto.

A higher proportion of the Native population lives in urban areas compared to the percentage of the African-American population that lives in cities. According to the American Community Survey results from 2010 to 2014, only 51% of Black Americans live in cities or small metropolitan areas. (39% were found to live in suburbs, and 10% in rural communities.) Since the Native population is much smaller than the Black population, when it comes to sheer numbers, there are far more Black people in American cities than Native people. But proportionate to their total populations, Native people are 20% more likely to live in cities than Black people.

Now that the demographic information is cleared up, I'll talk about why there are so many Native Americans in urban areas today.

Some cities have long had Native populations because the cities were built on Native people's lands and the Native people kept living there. Green Bay is a good example. While in 2010 Natives only comprised 4.1% of the population, in the mid-18th century, 81% of households were of Native or mixed-Native background. Over time, more and more migrants of different ethnicities came to these cities, at the same time that the Native population in the US was experiencing a decline (reaching its lowest point at 250,000 in 1900). The Indians in these cities never left, they just became a smaller and smaller proportion of the urban population.

Increased migration of Native peoples to cities began in the early twentieth century. Many thousands of Native children had been forcibly ripped from their homes and sent to residential schools. These schools embodied the motto "Kill the Indian, save the man" by seeking to assimilate Natives into white American culture. Many students returned home to the reservation after enduring the abusive schools, but others moved to cities to try to take advantage of their education for economic advancement.

Some of these urban migrants became important activists for off-reservation American Indian rights. Chicago became the centre of a group of activists led by Yavapai surgeon Dr. Carlos Montezuma. Living in Chicago, he worked as a physician at the infamous Carlisle Indian Industrial School from the late 1890s to 1923. Whenever Natives were passing through the city on business, Montezuma made a point of inviting them to his home and showing them hospitality, as well as helping them navigate the city's growing urban environment. Through his gregariousness, he built a network of activist-minded Natives in Chicago and other urban areas. He also worked hard at outreach to non-Native organizations and newspapers to spread awareness of the need for improved rights for Natives. He published a newspaper called Wassaja which had national circulation.

Montezuma's legacy meant that even after his death, American Indian activism in Chicago did not lose momentum. Three groups were founded shortly after his death in 1923: The Indian Fellowship League, the Grand Council Fire of American Indians, and the First Daughters of America, the last of which was part of the wider Illinois Federation of Women's Clubs. These groups were a parallel development to ethnic fraternities that developed in many American cities among European immigrant groups around the same time. These groups proved to be crucial networking and organizational tools for enterprising Indians following in Montezuma's wake, such as Grand Council Fire members Scotty Henry Peters (Ojibwe) and Oliver LaMere (Ho-Chunk). Another important Chicago activist of this period was the opera singer Tsianina Blackstone (Cherokee-Creek), who took advantage of her fame to advocate for Indian rights causes among politically progressive Chicagoans. All of this fed into the era of progressive social reforms of the early twentieth century.

After WWII, Indian migration to cities increased again. This was largely due to the federal policies of relocation and termination. Relocation meant that the federal government wanted to move Indians off of their reservation lands. Termination was a policy by which the federal government declared that a tribe's legal status was terminated, meaning that they no longer had any recognised sovereignty in negotiating with the United States, and their reservation was dissolved. The first tribe to undergo termination were the Menominee, as the Bureau of Indian Affairs decided that their successful lumber industry meant that they were economically self-sufficient enough to no longer need the federal government's support. The laws terminating the Menominee Nation were passed between 1954 and 1961.

Termination was an economic, political, and cultural disaster for tribes. The Menominee quickly went from being one of the wealthiest Native nations to the poorest county in Wisconsin. They had to sell off much of their land to pay for services that had originally been provided by the BIA as part of 19th century treaty agreements, since their treaties were no longer considered valid now that their tribal sovereignty had been dissolved. They went to the Supreme Court in 1968 after being told by a lower court that their hunting and fishing rights were no longer guaranteed by treaty. The Supreme Court upheld their treaty rights, and after a great deal of activism, the Menominee tribe was restored in 1973.

The period of twenty years when the Menominee were dissolved gives you a good insight of the cataclysm that hit communities like theirs in the postwar years. Without their tribal status being recognised, many were forced to leave the community to seek economic opportunity. Relocation and termination had a huge impact on Native migration to cities: At the start of WWII, more than 90% of Indians lived on reservations, while by the end of the 1960s, nearly half lived in urban areas. Relocation programmes provided job placements for Natives to move off-reservation, which provided another incentive to leave home. These jobs were usually for manual labour jobs with very poor pay. Urban Indian communities began to form which were overall much poorer than those of the early 20th century in places like Chicago. The issue of urban poverty among Natives was compounded by the white flight of the mid-20th century, in which affluent white city dwellers started to abandon cities for the suburbs.

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There's always more to be said, but in the meantime you may find some answers to your questions in this thread by u/enygma9753, specifically the complex historic relationship between the native peoples in Canada and the European settlers, colonial and later Canadian officials. It is a litany of broken promises, mistrust, systemic racism and bad faith agreements that alienated, disenfranchised and segregated the native peoples from society for years.

In Canada, the Royal Proclamation of 1763 -- created in the aftermath of the Conquest of Quebec -- set out the initial limits of white settlement in America, and the duties and responsibilities the Crown (aka the government of the day acting in the name of the king) has in its relationship with the native peoples. It's considered the "Magna Carta" of Crown-indigenous relations in Canada, and several court rulings have upheld this principle over the years.