Ibn Khaldun, the great Muslim historian, in his Introduction to History:
Taxation and the reason for low and high tax revenues
It should be known that at the beginning of a dynasty, taxation yields a large revenue from small assessments. At the end of the dynasty, taxation yields a small revenue from large assessments.
The same reason for this is that when the dynasty follows the way of Islam, it imposes only such taxes as are stipulated by the religious law, such as charity taxes, the land tax, and the poll tax. Theses have fixed limits that cannot be exceeded.
When the dynasty follows the ways of group feeling and (political) superiority, it necessary has at first a desert attitude, as has been mentioned before. The desert attitude requires kindness, reverence, humility, respect for the property of other people, and disinclination to appropriate it, except in rare instances. Therefore, the individual, the individual imposts and assessments, which together constitute the tax revenue, are low. When tax assessment and imposts upon the subjects are low, the latter have the energy and desire to do things. Cultural enterprises grow and increase, because the low taxes bring satisfaction. When cultural enterprises grow, the number of individual imposts and assessments mounts. In consequence, the tax revenue, which is in sum total of (the individual assessment), increase.
When the dynasty continues in power and their rulers follow each other in succession, they become sophisticated. The Bedouin attitude and simplicity lose their significance, and the Bedouin qualities of moderation and restraint disappear. Royal authority with its tyranny and sedentary culture that stimulates sophistication, make their appearance. The people of the dynasty then acquire qualities of character related to cleverness. Their customs and needs become more varied because of the prosperity and luxury in which they are immersed. As a result, the individual imposts and assessments upon the subjects, agricultural labourers, farmers and all the other tax payers, increase. Every individual impost and assessment is greatly increased, in order to obtain a higher tax revenue. Customs duties are placed upon articles of commerce and (levied) at the city gates. Then, gradual increases in the amount of the assessments succeed each other regularly, in correspondence with the gradual increase in the luxury customs and many needs of the dynasty and the spending required in connection with them. Eventually, the taxes will weigh heavily upon the subjects and overburden them. Heavy taxes become an obligation and tradition, because the increase took place gradually, and no one knows specifically who increase them or levied them. They lie upon the subjects like an obligation and tradition.
The assessments increase beyond the limits of equity. The result is that the interest of the subjects in cultural enterprise disappears, since they compare expenditure and taxes with their income and gain and see little profit they make, they loose all hope. Therefore, many of them refrain from all cultural activity. The result is that the total tax revenue goes down, as individual assessment go down. Often when decrease is noticed, the amounts of individual imposts are increased. This is considered a means of compensating for the decrease. Finally, individual imposts and assessments reach their limit. It would be of no avail to increase them further. The costs of all cultural enterprise are now too high, the taxes are too heavy, and the profits anticipated fail to materialize. Finally, civilization is destroyed, because the incentive for cultural activity is gone. It is the dynasty that suffers from the situation, because its profits from cultural activity.
If one understands this, he will realize that the strongest incentive for cultural activity is to lower as much as possible the amounts of individual imposts levied upon persons capable of undertaking cultural enterprises. In this manner, such persons will be psychologically disposed to undertake them, because they can be confident of making a profit from them.
In the later years of dynasties customs duties are levied
It should be known that at the beginning, dynasties maintain the Bedouin attitude, as we have stated. Therefore, they have few needs, since luxury and the habits that go with it do not (yet) exist. Expenses and expenditures are small. At that time, revenue from taxes pays for much more than the necessary expenditures, and there is a large surplus.
The dynasty, then, soon starts to adopt the luxury and luxury customs of sedentary culture, and follows the course that had been taken by previous dynasties. The result is that the expenses of the people of the dynasty grow. Especially do the expenses of the ruler mount excessively, on account of his expenditures for his entourage and the great number of allowances he has to grant. The (available) revenue from taxes cannot pay for all that. Therefore, the dynasty must increase its revenues, because the militia needs (ever) larger allowances and the ruler needs (ever) more money to meet his expenditures. At first, the amounts of individual imposts and assessments are increased, as we have stated. Then, as expenses and needs increase under the influence of the gradual growth of luxury customs and additional allowances for the militia, the dynasty is affected by senility. Its people are too weak to collect the taxes from the provinces and remote areas. Thus, the revenue from taxes decreases, while the habits (requiring money) increase. As they increase, salaries and allowances to the soldiers also increase. Therefore, the ruler must invent new kinds of taxes. He levies them on commerce. He imposes taxes of a certain amount on prices realized in the markets and on the various (imported) goods at the city gates. (The ruler) is, after all, forced to this because people have become spoiled by generous allowances, and because of the growing numbers of soldiers and militiamen. In the later (years) of the dynasty, (taxation) may become excessive. Business falls off, because all hopes (of profit) are destroyed, permitting the dissolution of civilization and reflecting upon (the status of) the dynasty. This (situation) becomes more and more aggravated, until (the dynasty) disintegrates.
Commercial activity on the part of the ruler is harmful to his subjects and ruinous to the tax revenue
Sometimes, the ruler himself may engage in commerce and agriculture, from desire to increase (his) revenues. He sees that merchants and farmers make (great) profits and have plenty of property. (He sees) that their gains correspond to the capital they invest. Therefore, he starts to acquire livestock and fields in order to cultivate them for profit, purchase goods, and (enter business and) expose himself to fluctuations of the market. He thinks that this will improve (his) revenues and increase (his) profits.
However, this is a great error. It causes harm to the subjects in many ways. First, farmers and merchants will find it difficult to buy livestock and merchandise and to procure cheaply the things that belong to (farming and commerce). The subjects have (all) the same or approximately the same amount of wealth. Competition between them already exhausts, or comes close to exhausting, their financial resources. Now, when the ruler, who has so much more money than they, competes with them, scarcely a single one of them will (any longer) be able-to obtain the things he wants, and everybody will become worried and unhappy.
Furthermore, the ruler can appropriate much of (the agricultural products and the available merchandise), if it occurs to him. (He can do it) by force, or by buying things up at the cheapest possible price. Further, there may be no one who would dare to bid against him. Thus, he will be able to force the seller to lower his price. Further, when agricultural products such as corn, silk, honey, sugar, and other kinds of agricultural products, or goods of any kind, become available, the ruler cannot wait for a (favorable) market and a boom, because he has to take care of government (needs). Therefore, he forces the merchants or farmers who deal in these particular products to buy from him. He will be satisfied only with the highest prices and more. (The merchants and farmers, on the other hand), will exhaust their liquid capital in such transactions. The merchandise they thus acquire will remain useless on their hands. They themselves will no longer be able to trade, which is what enables them to earn something and make their living. Often, they need money. Then, they have to sell the goods (that they were forced to buy from the ruler), at the lowest prices, during a slump in the market. Often, the merchant or farmer has to do the same thing over again. He thus exhausts his capital and has to go out of business.658
This becomes an often repeated process. The trouble and financial difficulties and the loss of profit which it causes the subjects, takes away from them all incentives to effort, thus ruining the fiscal (structure). Most of the revenue from taxes comes from farmers and merchants, especially once customs duties have been introduced and the tax revenue has been augmented by means of them. Thus, when the farmer gives up agriculture and the merchant goes out of business, the revenue from taxes vanishes altogether or becomes dangerously low.
Furthermore, (the trading of the ruler) may cause the destruction of civilization and, through the destruction and decrease of (civilization), the disintegration of the dynasty. When the subjects can no longer make their capital larger through agriculture and commerce, it will decrease and disappear as the result of expenditures. This will ruin their situation. This should be understood.
Amirs and other men in power in a country who engage in commerce and agriculture, reach a point where they undertake to buy agricultural products and goods from their owners who come to them, at prices fixed by themselves as they see fit. Then, they resell these things to the subjects under their control, at the proper times, at prices fixed by themselves. This is even more dangerous, harmful, and ruinous for the subjects than the afore-mentioned (procedure). The ruler is often influenced to choose such a (course) by that sort of people – I mean, merchants and farmers – who bring him into contact with the profession in which they have been reared. They influence the ruler to choose this (course). They work with him, but for their own profit, to garner quickly as much money as they may wish, especially through profits reaped from doing business without having to pay taxes and customs duties. Exemption from taxes and customs duties is more likely than anything else to cause one’s capital to grow, and it brings quick profits. These people do not understand how much damage is caused the ruler by each decrease in the revenue from taxes. The ruler, therefore, must guard against such persons, and not pay any attention to suggestions that are harmful to his revenues and his rule.