From the U.S. war cry in the mid-1840s over disputed British and American territory in the Pacific Northwest—"Fifty-Four Forty or Fight!"—to the westward extension of the Mason-Dixon Line separating slave from free states, boundaries and borders of various sorts preoccupy the nation during the antebellum decades. Debated, fought over, and painstakingly delineated on maps and charts, boundaries lie at the heart of major political decisions and prove fundamental to a host of social and economic issues. Paramount among such issues are the expansion of national borders as fresh territories are either annexed by diplomatic treaty or conquered outright, the relocation of eastern tribes to west of the Mississippi through the Indian Removal Act of 1830, the intensification of regionalism, the westward recession of the edge of settlement, and debate over whether new states added to the union should be slaveholding or free. As the nation...