In terms of the European states system, the ‘long nineteenthcentury’, between the end of the Napoleonic era and the outbreak of the First World War may conveniently be divided into three periods. The forty years between the Congress of Vienna and the outbreak of the Crimean War constituted the longest period of peace between the great powers since the states system emerged at the beginning of the sixteenth century. Whether it reflected simply a primitive instinct for selfpreservation in an era when the experience of the immense destruction and instability of the Revolutionary and Napoleonic Wars still exercised a hold over the minds of statesmen, or whether it embodied more far-sighted motives of enlightened self-interest and an appreciation that in the exercise of restraint by the individual members of the states system lay the best guarantee of the security of all, the post-1815 system, based on compromise, balance, and respect for a legitimate order established by treaties gave Europe forty years of peace. In terms of the alignments of the powers, the peace was upheld by a broad consensus between the members of the victorious coalition, centred on Austria. This weak, status quo power that depended on respect for legitimacy and treaty rights for its very existence, was able to serve effectively as the keystone of the system, so long as it could count on the support of one, or, ideally, both of the ‘superpower’ members of the coalition, Great Britain and Russia. It was the co-operation of this preponderant and fundamentally conservative group of powers that maintained the peace for a generation after 1815

and that defeated the assault launched on the established international order by the revolutionaries of 1848.