The war and the filibusters set a template, take the land and exclude the people, that outlived them by two centuries. The finale traces it from the Treaty of Guadalupe Hidalgo's broken promises and the dispossession of Mexican-American landowners through the 'greaser' laws and the Insular Cases to border and citizenship fights live in 2026. It then weighs where race explains the era best and where slavery-politics, commerce and contingency did the work.
Historians genuinely disagree about whether race, slavery-politics, commerce or contingency ranks first among causes, and about how much the war itself created a Mexican American racial identity. Present-day politics is treated as an attributed parallel, non-partisanly.