War Externalities of Livestock Money
Money is in some regards not uniform in its externalities. An appreciation of the value of the USD, for example, has other externalities that an appreciation of the value of gold. We know from history that gold vaults and mines have been obvious military objectives in war, and a price increase of that money magnifies the temptation to capture storage- and production centers.
The gold of nation states have always been defended by strategically located armies or militias. But what do you do when the very land you and your people walk on belongs to the monetary premium sphere of your warlike neighbors? It is likely that this phenomenon occurred among the 12th and 13th century Mongol states in North-Eastern Asia, who for a long period partly seems to have operated on a monetary livestock standard.
In The Cambridge Medieval History volumes, the following is said on the early 20th century Mongols and their animals:
In general, cattle-rearing is unknown to the severest kind of nomadism. The ox soon dies of thirst, and it has not sufficient endurance or speed for the enormous wanderings; its flesh has little value on the steppe. The animals actually employed for rearing and food are consequently the sheep (to a less extent the goat as leader of the sheep flocks), the horse, and here and there the ass; also, in smaller number, the two-humped camel (in Turan the one-humped dromedary as well) as beast of burden. [...]
A wealthy Mongolian possesses as many as 20 000 horses and still more sheep. Rich Kirghiz sometimes have hundreds of camels, thousands of horses, tens of thousands of sheep. 
That the wealth of these peoples were measured in livestock is an indication that it was indeed money at this time. The Cambridge Medieval History continues:
Instead of our gold and silver coinage they have sheep coinage, in which all valuations are made. Of course they were acquainted with foreign coins from the earliest times, and obtained countless millions of pounds from tribute, plunder, and ransom of prisoners, and they used coins, now and then, in external trading, but among themselves they still barter, and conclude all their business in sheep, cattle, horses, and camels. 
Also fines seems to have been fixed in livestock among some Mongol peoples:
Among the Kazak-Kirghiz anyone who killed a man of the plebs (a "black bone"), whether willfully or accidentally makes no difference, must compensate the relations with a kun (i.e. 1000 sheep or 100 horses or 50 camels). The slaughter of a "white bone" costs a sevenfold kun.
Not only was livestock blood money - it was likely used as a bride price as well. The documented travels of William de Rubruquis in the 1250's gave us some insight into early Mongol marriage traditions:
As touching mariages, your Highnes is to understand that no man can haue a wife among them till he hath bought her: whereupon sometimes their maids are very stale before they are married, for their parents alwaies keep them till they can sel them. 
British soldier and author of 'The Quest for Cathay', Percy Sykes, corroborated this as he was stationed by the Pamir Mountains in the 19th century. Here is what he had to say about the use of sheep money among the Mongols he met there:
Among the Kirghiz whom I met on the Pamirs the difficulty always was for the young fellows to find the hundred sheep which was the usual price for a girl, and one of my hunters, when paid off, counted his wages as representing so many sheep! 
So, if livestock was money, it must have had a monetary premium. Any monetary premium would, given all else equal, put an upward pressure on supply as it made it more profitable to breed or in other ways obtain livestock. If their own graze-lands were not enough, this monetary premium gave direct incentives for the Mongols to conquer new graze-lands.
Now, most evidence of livestock-money stems from the 19th and 20th century, but it is likely that the Mongols utilized a similar standard before acquiring China and other, more civilized nations. The slaughter they brought with them as they trampled these other societies was on a scale seldom seen before; it is estimated that many millions died as a result of direct executions or deliberate starvation. Einzig makes the point that the monetary premium of livestock-money directly contributed to the aggressiveness of the Mongols:
There can be no doubt that this search for new grazing lands was largely responsible for the aggressive expansionary policy of the pastoral races which were surging westward towards the end of the Ancient Period, and in particular of the Mongols towards the middle of the 13th century. It was largely because they chose to use livestock as their currency that they had to find more and more room for their livestock which tended to be well in excess of normal economic requirements. 
Some would argue that the ruthlessness of the Mongols was game-theoretic; any new foe knew what happened if they did not surrender. But this can not be the only explanation of the mass murdering, or other nations and tribes would have historically been equally harsh after conquering their neighbors. The livestock-money externality described above seems in other words plausible enough to warrant discussion.
 The Cambridge Medieval History, Volumes 1-5 (1936). Cambridge, University Press, p. 331.
 Ibid., p. 343.
 Ibid., p. 339.
 Percy Sykes, The Quest for Cathay (1936), London, A. and C. Black, p.103.
 Paul Einzig, Primitive Money (1949). London: Pergamon Press Ltd, p.274.