The small size of the Greek cities and their incapacity for acting in concert led to their subjugation by Macedonia in 338 B.C. About sixty or eighty years later many of them had recovered their independence, and some of them, in order to guard against a second conquest by Macedonia, joined together in a league or federation. The union of many communities in a federation was not a new thing in Greek history: during several centuries that preceded the year 338 B.C. some obscure tribes of mountaineers (the Achæans) had lived in such a union; their league had been broken up by the Macedonian conquerors, but they had been able, about 281 B.C., to reconstitute it: and the Greek cities, when they began, about 251 B.C., to see their need of mutual defence, had the Achæan League ready at hand, and were able to gain what they needed by enrolling themselves among its members. The Achæan League, enlarged by the admission of many important cities, was a federal state: that is to say, it was a community in which each city or canton had a government of its own for most purposes, but the federation or union of cities and cantons had also a common government for those matters which most nearly concerned the safety of them all. The League was perfectly successful till 221 B.C. in attaining the ends for which it had been established, and is remarkable as furnishing the first example in history of a well organized federal state[8]. [8] For details see Chapter VII. The Romans employed the strength, which they had acquired through their conquest of Italy and their success in the second Punic war, in getting possession of many distant territories inhabited by alien races. Before 146 B.C. they were masters of Macedonia, part of Asia Minor, Spain and northern Africa, and the Roman dominions presented an example of a mere political aggregate, or heterogeneous empire or number of peoples having no natural attraction for one another and held together only by force. For the rule of a heterogeneous empire the institutions of a city and even of an expanded city proved utterly unsuitable: and it was necessary that both the conquering city and the dominions which it had conquered should submit to be ruled under a centralised and despotic system of government adapted to the needs of a heterogeneous empire. The right system was only gradually made, but it had been completed by the death of the Emperor Constantine the Great in 337 A.D.