There are secessionist movements in all parts of the world, encompassing both democratic and non-democratic countries. It is typically thought that this important phenomenon is regulated by international law alone. But, this article argues that when looking anew at constitutional law through the lens of secession, democracies’ weak spots are revealed. While political actors and scholars traditionally believe that bans on political parties ('militant democracy') and constitutional eternity clauses (`unconstitutional constitutional amendment`) are used and justified to protect democratic values alone, they are in fact also used to fight against secession. Democracies have been able to conceal their fight against secessionists, by creating a large gap between “the law on the books” and “the law as practiced.” This raises paradoxes so extreme, the democracies begin to appear to be using the tools of authoritarian regimes. In addition to exposing the facts on the grounds, the article also makes two normative claims: First, it argues that secession reveals the ways in which both doctrines—the ban and eternity clauses—are inextricably intertwined. This assertion is general and goes beyond the secession context. Second, the article argues that secession is helpful in revealing the intricate relationship between constitution-making and constitution-amending powers. Even those who hold that the power to amend the Constitution should be treated as equal to the constitution-making power may find that an exception is needed in the secession context. Secession may be regarded as an annihilation of the Constitution because it redefines the sovereign bodies. As such, secession necessitates extra-constitutional mechanisms. Contrary to the prevailing understanding that it is sufficient to garner the support of the seceding population, secession may require the independent deliberate consent of two new peoples—the seceding as well as the remaining population. Studying the delicate dance of constitutional democracies and secessionist movements not only enables a better understanding of constitutional law but may also shed new scholarly light on assumptions that Constitutions are generally silent about secession and may even implicitly allow it.