Hämäläinen's project here is very much grounded in political and diplomatic history, and as such may for some readers seem to have a bit of a musty, antique aura. Taken on its own terms, I think this book succeeds at a lot of things. Hämäläinen is very good at describing geographical space using concepts like technological and ecological frontiers, buffer zones and areas of effective control, and demographic fracture/displacement/migration to thoroughly redraw the map of the political realities of the North American interior in the 17th-19th centuries; for those of us still laboring under the weight of the conventional maps and boundaries we memorized in high school, this may be his most valuable contribution. He is also successful in giving a striking account of Lakota governance over time, describing a fluid political order which underwent many changes as the Lakota detached themselves from the eastern Sioux nations near the Great Lakes, consolidated themselves in the Missouri River valley, adapted to a new environment and carved out an extensive sphere of influence in the plains, and continued to drift northward and westward when confrontation with the post-civil war United States reached its peak.  Hämäläinen also emphasizes the long time-horizons under which the Lakota strategic vision operated and makes good account of the role of ecological resources, namely game. Finally, I think Hämäläinen strikes a good balance in devoting roughly equal attention to Lakota-US/European relations and intra-indigenous relations, understood as influencing one another but never fully blending into one another (at least not until the very end).

Although the earlier portions of Lakota America are interesting, and essential to the story of geographic drift, the actual historical inquiry feels stronger towards the latter half of the book, in which Hämäläinen is able to draw more extensively on Lakota sources (namely Winter Counts) and clearly describe the differing inclinations and political/diplomatic strategies of individual Lakota leaders (especially Red Cloud, Spotted Tail, and Sitting Bull). The earlier history, which seems to rely more on frontier narratives, is useful, but the source material available does limit my ability to fully credit all of Hämäläinen's proposals or interpretations.

Although I haven't been able to find as many grassroots Lakota responses to Hämäläinen's book as I would like, one point of controversy in its reception has been Hämäläinen's use of the term "empire" to describe the polity created by Lakota after migrating westward from a more condensed area in the Missouri and Minnesota river valleys. The term "empire" is worth problematizing; Lakota expansionary warfare against Crows, Shoshone, and others notwithstanding, the historical context in which the Lakota polity arose and operated was very distinct from the context in which "empires" of settler-colonialism constituted themselves. Ultimately, I don't think Hämäläinen is particularly interested in wading into this conceptual issue; he seems to be using the term "empire" mostly as a shorthand indicating extensive territorial power and diplomatic/strategic/historical agency (and because he used the term "empire" in regards to Comanche history in his previous book). I think Hämäläinen's discussion of the Lakota polity is specific enough that the word is unnecessary, and that he might have avoided valid concerns towards the political implications of his work by omitting it.

Lakota America moves at a measured, detail-oriented pace until reaching the Battle of Little Bighorn. After the Battle, Hämäläinen wraps up quickly, describing the final subjugation of Lakota power in the 1880s and 1890s in much scantier detail before adding a welcome but somewhat halfhearted epilogue about Lakota presence in contemporary struggles for Native American sovereignty from the AIM/Red Power movements to Standing Rock. I don't think choosing to end his core historical work at Little Bighorn is a problem; Hämäläinen's interest is the sociopolitical and geopolitical evolution of sovereign Lakota power in the American interior, and Little Bighorn is a valid end point for this story. Still, some readers may find a stronger conclusion wanting.