© 2015 International Studies Association. This is the peer reviewed version of the following article: Explaining Durable Diversity in International Systems: State Company and Empire in the Indian Ocean, International Studies Quarterly, Vol. 59(3), pp. 436–448, 2015. which has been published in final form at 10.1111/isqu.12197. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving (http://olabout.wiley.com/WileyCDA/Section/id-820227.html#terms)