Mapping the International System(s) of the 19th and 20th Centuries: A Contribution to Existing Datasets on Sovereign States

Abstract

We argue that the existing datasets on sovereign state membership possess two weaknesses: a requirement that states maintain diplomatic relations with Britain and France, and a size inconsistency that disqualifies many mid-sized states in the pre-1920 period. As a consequence, entire state systems are excluded from the data, and the total number of states during the 19th century is undercounted. We offer an alternative set of criteria that identifies 98 new sovereign states, and a total of 360 states between 1816 and 2011. These modifications reveal a previously overlooked pattern: the global trend in the number of states over time is concave. From a high of 131 states in 1816, the number fell precipitously in the mid-19th century as states became fewer in number and bigger on average through the processes of accession, conquest, and unification. This pattern of state consolidation bottomed out in the early 20th century, and states have proliferated since 1945.