This paper examines how changes in textbook adoption rules shaped historical narratives in American history textbooks between 1870 and 1930. During this period, most Western and Southern states transitioned from local to state-level textbook lists. We investigate whether it enabled regional interest groups such as United Daughters of the Confederacy to influence how publishers portrayed Civil War and the South. Using a novel dataset of 351 editions of middle-school history textbooks, we employ large language models to systematically measure pro-Southern slant across 75,000 text passages. Leveraging variation in the timing of state adoption laws, we find that state-level consolidation led to 18.5% more pro-Confederate coverage of the Civil War, with effects emerging 5-10 years post-adoption. This increase is partly driven by more positive portrayals of Confederate army leaders which was an explicit long-run objective of the United Daughters of the Confederacy activity. In addition to Southern publishers revising narratives to sell more textbooks in the South, some Northern publishers did so as well, resulting in greater exposure to pro-Southern content in some Western and Midwestern schools. Preliminary analysis using 1936-1945 Gallup survey data suggests that cohorts exposed to these biased textbooks during schooling exhibited more white supremacist attitudes later.