Were the ratio between the life of antagonism with alien societies, and the life of peaceful co-operation within each society, a constant ratio, some permanent compromise between the conflicting rules of conduct appropriate to the two lives might be reached. But since this ratio is a variable one, the compromise can never be more than temporary. Ever the tendency is toward congruity between beliefs and requirements. Either the social arrangements are gradually changed until they come into harmony with prevailing ideas and sentiments; or, if surrounding conditions prevent change in the social arrangements, the necessitated habits of life modify the prevailing ideas and sentiments to the requisite extent. Hence, for each kind and degree of social evolution determined by external conflict and internal friendship, there is an appropriate compromise between the moral code of enmity and the moral code of amity: not, indeed, a definable, consistent compromise, but a compromise fairly well understood. This compromise, vague, ambiguous, illogical, though it may be, is nevertheless for the time being authoritative. For if, as above shown, the welfare of the society must take precedence of the welfares of its component individuals, during those stages in which the individuals have to preserve themselves by preserving their society, then such temporary compromise between the two codes of conduct as duly regards external defense, while favoring internal co-operation to the greatest extent practicable, subserves the maintenance of life in the highest degree; and thus gains the ultimate sanction. So that the perplexed and inconsistent moralities of which each society and each age shows us a more or less different one, are severally justified as being approximately the best under the circumstances. But such moralities are, by their definitions, shown to belong to incomplete conduct; not to conduct that is fully evolved. We saw that the adjustments of acts to ends which, while constituting the external manifestations of life, conduce to the continuance of life, have been rising to a certain ideal form now approached by the civilized man. But this form is not reached so long as there continue aggressions of one society upon another. Whether the hinderances to complete living result from the trespasses of fellow-citizens, or from the trespasses of aliens, matters not; if they occur there does not yet exist the state defined. The limit to the evolution of conduct is arrived at by members of each society only when, being arrived at by members of other societies also, the causes of international antagonism end simultaneously with the causes of antagonism between individuals.