"Historians have been particularly interested in the fact that on two occasions during our period great empires provided security and a market for luxuries in different parts of the Indian Ocean world. The huge trade between China and the Abbasid empire has been linked to the rise and florescence of the Abbasid state after 750, and a similar situation with the T'ang dynasty in China from 618–907. The Fatimids in Egypt, the Colas in South India, and the Song in China produced the same effect in the eleventh and twelfth centuries.
There certainly seems to be some connection between flourishing trade and stable empires, albeit one hard to quantify. Such empires usually got most of their revenue from the land, not the sea, and prevailing norms were usually hostile, or at least indifferent, to sea trade and merchants. Yet merchants did provide customs revenues, and perhaps more important brought curiosities and preciosities to the court. More generally, a strong, stable empire obviously has advantages for economic activity in general, including sea trade. Some states were actually quite interventionist. Srivijaya controlled the straits of Melaka for some time. In the early eleventh century the Cola state in south India responded to this with devastating raids. Thirteen ports in the Malay peninsula, Sumatra and the Nicobar Islands were attacked by Rajendra Cola.
The decline of empires usually produces much confusion, and this may be detrimental to trade, though on the other hand as an empire declines it will release hoarded wealth with which to defend itself, thereby increasing liquidity. Some notable episodes in the decline of these empires no doubt did impact on trade. In its last few decades the T'ang dynasty was less stable, and Guangzhou was sacked and foreign merchants massacred in 878 by a rebel army. At this same time, in 868–83, the Zanj slaves in lower Mesopotamia rebelled, and this is considered to have contributed to Abbasid decline. Later, the coup de grâce for the Abbasids, that is the sacking of Baghdad by the Mongols in 1258, may have disrupted trade, though this claim is open to doubt. The other great example of politics intervening in the ocean in our period is the cessation of Zheng He's voyages in the 1430s as a result of a change in Ming policy. The precise reasons for this shift have been much debated, but certainly these expeditions were terminated by the court, and foreign trade greatly restricted. However, this coincides with the rise of Melaka, and it is a ‘chicken-and-egg' matter as to whether the rise of Melaka meant the great expeditions were no longer needed, as compared with the rise of Melaka being to fill the gap left by the end of the voyages. In any case, the whole matter of this connection is difficult indeed to prove. Perhaps the point to keep in mind is that there were much more constant and important matters which affected merchants engaged in sea trade, namely did their imports meet local demand, and were prices high?…"
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