From Catalonia to Kurdistan, Crimea to California, and Scotland to St. Kitts, secession has become a hotly debated political issue. While secessionist disputes appear to hinge on high power politics, they also have an important constitutional dimension. This Article offers a comprehensive exploration of how the world’s constitutions treat secession, and how constitutional secession clauses can affect real-world secessionist disputes. Drawing on an original dataset that captures how the world’s constitutions have dealt with secession from 1789 to 2015, we make a number of contributions.

First, we document the various ways in which constitutions have dealt with secession. While the bulk of the literature has been focused on a right to secession, such clauses are exceedingly rare in constitutions today, and most of the countries that constitutionalized such a right have broken up. Instead, where constitutions deal with secession, they tend to prohibit it, either by banning it explicitly or through an implicit prohibition that emphasizes territorial integrity. Other constitutions remain silent on the matter, even when there are live secessionist disputes. We provide a taxonomy of these various approaches and show how they have changed over time.

Second, we provide an analysis of how constitutional design choices about secession can have important real-world consequences. We develop a theory of how different constitutional design choices can affect downstream mobilization for secession. We test this theory empirically by replicating a number of existing studies, to which we add our own new data. Granting a right to secession, we find, is associated with a higher chance of a nation breaking up, and makes such break-ups less violent. By contrast, a clear and explicit prohibition of secession decreases popular support for secessionist movements and reduces associated violence, thus reducing the odds of a nation breaking up. Perhaps the worst option is for the constitution to remain silent on secession. Where the constitution is silent on secession, we find that secessionist movements are motivated to seize on this ambiguity and are able to garner popular support for the movement. Yet, these movements are surrounded by relatively high levels of violence, as central governments end up opposing the claim or the country’s highest court rules that it is without constitutional basis. We find similar results for implicit prohibitions: they increase both popular support and secessionist violence. Overall, these findings suggest that constitutional ambiguity can be harmful: it allows secessionist movements to garner support, but produces higher level of violence without improving the chances of success. We further probe these findings by studying two recent high-profile secessionist disputes: Catalonia in Spain and Kurdistan in Iraq, which confirm our findings.

Our findings have important real-world implications for constitutional drafting. As a number of countries are debating various degrees of autonomy for regionally clustered minority groups, our findings suggest that it is important to address the question of secession head-on and that careful constitutional drafting can avoid violence and instability.

Tom Ginsburg & Mila Versteeg, From Catalonia to California: Secession in Constitutional Law, 70 Alabama Law Review, 923–985 (2019).