Hi Edyz,
I will focus more on the late Comnenus period where the trade fortunes really slipped out of the Byzantines. The Byzantine Empire during the Comnenus dynasty was still rich and powerful. True, some Byzantines did start to lose the competition (partly because the Byzantine merchants were too much regulated by the government; trade was just means to an end for the Byzantines (for the Italians that was the end :) ) and perhaps because the Italian free cities only priority was trade while the Byzantine government had many other worries). Despite the fact that Italian merchants became influential, the Empire still kept some degree of control. How would you explain that the revenge of the Venetians came with 20 years delay. The Byzantine Empire under the Comnenus dynasty was strong. I think the decline began in the later years of the rule of Manuel I but it became obvious during the regency of Alexius II (1180-1183) when the unpopular regency prepared the tragedy that is going to happen. The Byzantine Empire is as strong as its Emperors. Without a strong leader, the Empire started to disintegrate (Antioch lost, the Armenians of Cilicia as well, Turkish raids, corruption). Then it comes the "messiah" Andronicus I who offered easy solutions and cleansing the Empire of all the foreigners and the corruption. Needless to say, slaughtering of the Italians in the capital and the harsh treatment of the aristocracy (i.e. the officers of the army) did not make the situation better. It was not long before the Andronicus was torn into pieces and the Angelus disaster came. Further fragmentation followed. Bulgaria and parts of Asia Minor were lost. Central control was so weak that towards the end of the Angelus dynasty the Emperor had to use non military ways to remove its enemies (bribes, assassination and intrigues). Soon after the Venetians and the crusaders sacked Constantinople.
Is it surprising that in times of disintegration, corruption and massacres the role of the Byzantine merchant lessened? Now here is the funny part. Perhaps the biggest contribution of the Angelus dynasty was that through marriage of the Emperor's daughters it paved the way for the Lascaris dynasty (1204-1261). While the Nicaean Empire lost a lot of the important trade posts in the Mediterranean (Constantinople included), its economy was surprisingly healthy. The local merchant and artisans were supported and agriculture flourished. Perhaps because the Turkish and Latin threat were neutralized in the very beginning of the Lascaris dynasty. It was one of those critical moments when desperate times required desperate measures and the aristocracy stood behind a capable leader (Theodore I and John Ducas Vatatzes).
And then again, another unpopular regency and Michael VIII (1259- 1282) came into power with a new dynasty. Constantinople was reconquered but the economy did not flourish. Why? If we look how much money the Empire spent for campaigns and bribes, if we look at the internal situation in the Empire (a new dynasty after the blinding of the legitimate emperor), we may understand why. Bribes and gifts to the Golden Horde in what is now Russia and Ukraine, to Hulagu in Iran, the expensive (and still very successful) sponsorship for the Sicilian Vesper rebellion, campaigns in Greece, campaigns against Bulgaria (some even reaching the Bulgarian capital). The internal situation: a new dynasty: the loyalty of the aristocracy and church needed to be bought. Privileges were given away, tax exemption and lavish infrastructure projects in Constantinople. Eventually in the reign of Andronicus II, the Empire had little resources to defend its heart: the Asian Minor provinces. Refugees, loss of territories and on the top of that, even higher taxes. The Byzantines were also forced to rely on the naval support of the Italians which worsened the situation even more (no/little taxes on Italian merchants). Is it surprising that the Byzantines lost their positions in the Mediterranean? What kind of economy would stay healthy when the provinces separate or are being conquered, every 10 years there is a massacre or a crusade (or both), corruption and increasing taxation?
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