When the General Assembly (GA) Hall of the United Nations headquarters first opened in 1952, it had 70 seats for 47 members, with the expectation that its membership would increase in the future.1 Today, it seats members from 192 countries. This change reflects the precipitous growth in the number of states in the international system over the past half-century. Whereas new states in the past seemed likely to form via merger as opposed to dissolution or secession, the growing demand for seats in the GA chambers is indicative of a relatively new trend in state formation: secession is, and has been, on the rise.
To hear that secession is increasingly common is not unusual. But this trend has not been previously documented in a systematic manner, nor has it been explained. We seek to remedy this gap by drawing on existing data to illustrate the basic premise that secession, in which part of a sovereign state breaks away to form a new sovereign state, is more common today than in past eras. We examine changes in the number of states in the international system, in the number of new states emerging via the process of decolonization as opposed to secession from contiguous states, and in the number of secessionist movements in the system. We then turn to explanations for these trends. Why did secession become relatively common in the twentieth century?
Will it continue as the primary mode of state formation in the twenty-first century? Is there an end