That is the new wonderful and stunning book by Pekka Hämäläinen, here is one excerpt from the opening section:

Two centuries earlier, in the middle years of the seventeenth century, the Lakotas h ad been an obscure tribe of hunters and gatherers at the edge of a bustling new world of Native Americans and European colonists that had emerged in the Eastern Woodlands of North America. They had no guns and no metal weapons, and they carried little political clout, all of which spelled danger: the odds of survival were slim for people who lacked access to Europeans and their new technologies of killing. That crisis set off what may be the most improbably expansion in American history. Lakotas left their ancient homelands and reinvented themselves as horse people in the continental grasslands that stretched seemingly forever into the horizon. This was the genesis of what I call Lakota America, an expansive, constantly transmuting Indigenous regime that pulled numerous groups into its orbit, marginal and dispossessed its rivals — both Native and colonial — and commanded the political, social, and economic life in the North American interior for generations. Just as there was Spanish, French, British, and the United States of America, there was Lakota America, the sovereign domain of the Lakota people and their kin and allies, a domain they would protect and, if necessary, expand. A century later, the Lakotas had shifted the center of their world three hundred miles west into the Missouri Valley, where they began to transform into a dominant power. Another century later they were the most powerful Indigenous nation in the Americas, controlling a massive domain stretching across the northern Great Plains into the Rocky Mountains and Canada.

…Yet they never numbered more than fifteen thousand people.