Journal Article

Coalition Formation in Non-Democracies

Daron Acemoglu, Georgy Egorov and Konstantin Sonin

in The Review of Economic Studies

Published on behalf of Review of Economic Studies Ltd

Volume 75, issue 4, pages 987-1009
Published in print October 2008 | ISSN: 0034-6527
Published online October 2008 | e-ISSN: 1467-937X | DOI: http://dx.doi.org/10.1111/j.1467-937X.2008.00503.x
Coalition Formation in Non-Democracies

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We study the formation of a ruling coalition in non-democratic societies where institutions do not enable political commitments. Each individual is endowed with a level of political power. The ruling coalition consists of a subset of the individuals in the society and decides the distribution of resources. A ruling coalition needs to contain enough powerful members to win against any alternative coalition that may challenge it, and it needs to be self-enforcing, in the sense that none of its subcoalitions should be able to secede and become the new ruling coalition. We present both an axiomatic approach that captures these notions and determines a (generically) unique ruling coalition and the analysis of a dynamic game of coalition formation that encompasses these ideas. We establish that the subgame-perfect equilibria of the coalition formation game coincide with the set of ruling coalitions resulting from the axiomatic approach. A key insight of our analysis is that a coalition is made self-enforcing by the failure of its winning subcoalitions to be self-enforcing. This is most simply illustrated by the following example: with “majority rule”, two-person coalitions are generically not self-enforcing and consequently, three-person coalitions are self-enforcing (unless one player is disproportionately powerful). We also characterize the structure of ruling coalitions. For example, we determine the conditions under which ruling coalitions are robust to small changes in the distribution of power and when they are fragile. We also show that when the distribution of power across individuals is relatively equal and there is majoritarian voting, only certain sizes of coalitions (e.g. with majority rule, coalitions of size 1, 3, 7, 15, etc.) can be the ruling coalition.

Keywords: D71; D72

Journal Article.  16322 words.  Illustrated.

Subjects: Analysis of Collective Decision-making

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