Internet topology reflects economic and political constraints that change over time. Although autonomous systems (AS) topology has been measured and modeled for many years, focusing primarily on economic relationships, earlier studies have not quantified how topology is changing with respect to nation-state boundaries. National boundaries are natural points of control for surveillance, censorship, tariffs and data localization. This paper introduces a measure, national chokepoint potential (NCP), to characterize how a country’s AS topology is organized in terms of BGP paths that can carry traffic across international borders. To study country-level chokepoints, we developed BGP-SAS, an open source, cross platform, efficient set of tools for simulating BGP routing and calculating national chokepoint measures. We use these tools to assess how AS topologies have changed over a ten-year span, finding significant variability among countries, with some increasing their chokepoint potential and others remaining constant, fluctuating, and in some cases declining. Overall, however, most national Internet boundaries have either become more pronounced or remained constant, despite new infrastructure buildouts and increased Internet usage. When compared to independent measures of Internet freedom, we find statistically significant relationships between NCP and Internet freedom.