Many years ago, when studying economics, I came across a concise statement explaining how wealth is created:
Wealth is created when resources are moved from lower-value uses to higher-value uses.
I was reminded of it when, while reading a post about the crusades, I came across this excerpt from Gibbon:
In one respect I can indeed perceive the accidental operation of the Crusades, not so much in producing a benefit, as in removing an evil. The larger portion of the inhabitants of Europe was chained to the soil, without freedom, or property, or knowledge; and the two orders of ecclesiastics and nobles, whose numbers were comparatively small, alone deserved the name of citizens and men.
This oppressive system was supported by the arts of the clergy and the swords of the barons. The authority of the priests operated in the darker ages as a salutary antidote: they prevented the total extinction of letters, mitigated the fierceness of the times, sheltered the poor and defenceless, and preserved or revived the peace and order of civil society.
But the independence, rapine and discord of the feudal lords were unmixed with any semblance of good; and every hope of industry and improvements was crushed by the iron weight of the martial aristocracy. Among the causes that undermined the Gothic edifice, a conspicuous place must be allowed to the Crusades. The estates of the barons were dissipated, and their race was often extinguished, in these costly and perilous expeditions.
Their poverty extorted from their pride those charters of freedom which unlocked the fetters of the slave, secured the farm of the peasant and the shop of the artificer, and gradually restored a substance and a soul to the most numerous and useful part of the community. The conflagration which destroyed the tall and barren trees of the forest gave air and scope to the vegetation of the smaller and nutritive plants of the soil. [Decline and Fall, Ch. LXI]
The reduction in the extractive power of the feudal lords, who had wasted the social surplus on military equipment and adventures, allowed the creators of the wealth to hold on to more of it, and to invest it in productive enterprises, so that over generations it multiplied. Modern society is in large part a result of this productive investment.