In this study, we explore the long-run effects of Swedish and Polish–Lithuanian imperial legacies in the Baltic region. Using a robust regression discontinuity design, we identify persistent differences in socio-economic development across the South Livonia–Courland and the South Livonia–Lettgallia borders that emerged as a result of the Altmark Truce (1629) between Sweden and Poland–Lithuania. We find that there is a positive post-imperial persistence of the Swedish legacy that explains modern Baltic development. Our results are robust to the RD estimation of the post-1629 Swedish–Swedish border between North Livonia and Estland, the Pale of Settlement, spatial noise, placebo outcomes, and the introduction of a quadratic polynomial, as well as different bandwidths. Higher historical shares of Lutherans, Germans, and landowners may predict higher levels of contemporary socio-economic development in the Swedish partition of South Livonia than in the Polish–Lithuanian partitions of Courland and Lettgallia.
