 Important developments in political thinking and practice took place under the Hellenistic kingdoms that supplanted Macedon in its suzerainty over the formerly independent Greek city-states. These included, for example, a genre of rhetorical letters addressed to rulers, and the important analysis of Greek and Roman constitutional change by the second-century Greek historian Polybius (Hahm 2000). As kingships flourished among the Hellenistic kingdoms until they in turn came under Roman rule, not only the value of political participation, but also the proper domains of politics, were widely debated. Different authors would orient themselves respectively to still-surviving polis communities and the various leagues which united many of them in the Hellenistic period; to the kingdoms mentioned above; to the Roman constitution, and eventually to the special forms of imperial power which eventually arose therein; and in more philosophical terms, to the cosmos as a whole and all rational beings within it.