Quotations from Chapter 34 of Edward Gibbon's History of the Decline and Fall of the Roman Empire ("The Character, Conquests, and Court of Attila, King of the Huns; Death of Theodosius the Younger; Elevation of Marcian to the Empire of the East (376-453 A.D.)"):
The laws of war, that restrain the exercise of national rapine and murder, are founded on two principles of substantial interest: the knowledge of the permanent benefits which may be obtained by a moderate use of conquest, and a just apprehension lest the desolation which we inflict on the enemy's country may be retaliated on our own. But these considerations of hope and fear are almost unknown in the pastoral state of nations.
(see also Gibbon _-_Table_of_Contents, Gibbon_-_Thoughts_Upon_Reading, ... and http://www.his.com/~z/gibbon.html for a single-page presentation of Gibbon quotes)
(correlates: Gibbon - Table of Contents, JustLayers, GibbonChapter27, ...)