To the Mongols, wealth is measured by how many horses and sheep you have. Gold and money meant nothing to them.
Their horses are small but tough and strong in endurance.
When the empire expanded, they had a mail service similar to the pony express where messages can get across quickly and get almost immediate backups and support during war.
Their army was always outnumbered but thanks to their superior manoeuvre and bows and arrows, they normally exterminate enemies with heavy equipment and armour.
One armed Mongol has several ponies for transport or war. If a pony in injured, it becomes food for the army.
Ponies also provide warmth during winter.