A state formed by colonial expansion presents difficulties to any one who tries to define its nature. It is like a family of plants all sprung from one stock; the stock has sent out offshoots, which have themselves struck root, but are still connected with the parent stock from which they sprang. In one sense such an expanded state is still a single political community: in another sense each of the colonies which belongs to it is also a political community, though it never possesses complete independence, and therefore is not to be counted as a state. The greatest conquerors of distant lands outside Europe have been the Spaniards, the English and the Russians. Their conquests formed three great political aggregates or heterogeneous empires, the Spanish Empire in southern and central America, the Indian Empire, and the Russian Empire. The Indian and the Russian Empires are administered by methods more or less resembling those used in the old heterogeneous Empire of the Romans by Constantine the Great and his successors: the administration of the Spaniards was very defective from the outset, and at the beginning of the nineteenth century their empire broke up into a number of independent states. And now I may attempt a classification of all the more important forms that have been assumed by groups or collections of men living under governments. First of all, some of these groups are mere political aggregates, having little in common save the fact of living under one government, and the rest are political communities whose members have much else beside government in common. The mere aggregates will not need to be further divided; they are all heterogeneous empires held together by force. The political communities must be divided into three classes, tribes, cities, and the larger political communities. The class tribes needs no subdivision: cities must be divided according as they are inexpansive or expansive: the larger political communities (a class identical with the nations and those communities which possess many of the qualities of nations) need be subdivided only into unitary states or large political communities each with a single government only, and federal states or large political communities in which there is one government for some purposes and many governments for other purposes. The essentials of a perfect classification are four in number. Firstly, it ought to be exhaustive or to comprehend all individual specimens, so that no individual shall be without a place in it. Secondly, the marks which distinguish the classes should be easily recognisable. Thirdly, the marks of one class should never be present in a single individual together with the marks of another: for, if they are, the individual is in two classes at once. Fourthly (and this is most essential of all), the classes should be such that many important general propositions are true of all the individuals which compose any given class.