They are supposedly of Caddoan stock but are also Anishinabe. To understand the Anishinabe Arikara, read William Clark's (the William Clark of the Lewis and Clark Expedition) account about the Indians in the Kansas-Oklahoma-Texas region. White historians claim that the Arikara moved up to the North Dakota region from a location further south where the Caddoan people lived. Anishinabe soldiers forced their way into Caddoan country and subdued them. They formed alliances with them and brought some up to the North Dakota and South Dakota region, where a large Anishinabe population existed. Though subjugated by the powerful Anishinabe Nation, the Arikara were dealt with by the Anishinabe Nation in a loose manner. As long as a tribute was paid to the Anishinabe Nation, Anishinabe ogimak paid little attention to the Arikara and offered to protect them. Exactly when the Arikara reached the North Dakota region is not precisely known. They are closely related to the Caddoan Pawnees. Clark named these people who the whites refer to as being of Caddoan origin, as the Chippaway. He also said they were known by other names including O-jib-a-no and Saulteaux (pronounced as "soe-toe"), which are obviously known of by the Anishinabe people. Clark said they spoke a language he called Chippaway. Arikara Indians and all other Caddoan Indians, are very important to the Anishinabe people. And you know why now! So the Chippaway Indians are not Chippewa's? Google "Chippaway" and you'll learn that it was used by the whites in the 18th and 19th centuries, to refer to the Chippewa's of the Ohio region and elsewhere.
You can also visit the Lewis and Clark Jouranals website with information about the Chippaway people by clicking this link. After you get to the page, scroll down and you'll notice Clarks information on 72 different groups of Native Americans. Numbers 46 through 50, are about the Chippewa's who lived in the Minnesota region. Clark called them Chipaways, or Algonquin's, or O-chi-pa-wa, or Soe-toe (Saulteaux), or as he spelled the name Souteau, Souteaus, Souteu, Souters, Souteaux. Number 53 is about the Chippaway people. Clark also said they were known as Pania which is the Pawnee Tribe of course. The Chippaway or Arikara, are really the Black River and Swan Creek Chippewa's. They subdued the native Indians of the Kansas-Oklahoma-Texas region. However, an earlier group of Anishinabe people from the Montana-Wyoming region invaded the Oklahoma-Texas region in the 17th century. That means that there are two different groups of Chippewa's we have to pay careful attention to.
After the United States commenced to negotiate with the Anishinabe Nation (that part of the Anishinabe Nation which lived on the Great Plains), they used illicit means to force their way out on to the Great Plains. One of those illicit means was to separate the many different Indian Nations subjugated by the powerful Anishinabe Nation, from their Anishinabe subjugators. They lied to the many Indian Nations subjugated by the Anishinabe Nation, especially about recognizing that each of the Indian Nations subjugated by the Anishinabe Nation had their own country (territory). The United States did that through the 1851 Fort Laramie Treaty. A series of wars were fought in the northern plains, between 1850-1880, in which some of the Arikara joined with the Anishinabe soldiers to fight the whites. Most Arikara may have stayed neutral but they faced an Anishinabe Nation which probably would have thought it wise to punish the Arikara for disloyalty. Anishinabe ogimak made it clear to the Caddoan people that they would protect them and their land. They did that through a treaty agreement.
So in all likelihood the Arikara people were compelled to join with Anishinabe soldiers to fight the whites. After the 1876-1877 Black Hills War and Nez Perce War ended, the Arikara people were split. One group continued to defy the whites, while the other group chose to join those Anishinabek and Dakotas, and settled down to live peacefully in western South Dakota, and on the large Fort Berthold Reservation of North Dakota. The hostile Arikara moved up to where Fort Buford was located and the nearby location where the future Fort Peck Reservation would be located. In reality they have not surrendered. I admit that because of Ogima Little Shell's refusual to sign the 10 cent an acre treaty, which really was a treaty to force the Anishinabe Nation to legally eradicate the huge Reservation (the Promised Land) the United States set aside for the Anishinabe Nation and their Indian allies. Today, the Arikara Tribe lives on the Fort Berthold Reservation of North Dakota and on the Standing Rock-Cheyenne River Reservation of North Dakota and South Dakota. They also live on the Trenton Reservation of Montana and North Dakota. It is also known as the Turtle Mountain Reservation and Trenton Indian Service Area. However, the whites have forced them to lose their tribal identity. The Arikara are really Anishinabek who absorbed many Caddoan peoples. Their population is among the 8,400 citizens of the Fort Berthold Reservation.