There was political tension between different classes developing from the growth in wealth and influence of the merchant trading class. Thucydides refers to the political change and unrest that evolved with an expansion of trade and growing wealth in some parts of Greece. Traders played a significant role in the general movement, which resulted in the Greek colonies. It was they who knew where the land was available and traders were interested in a colony, which could be a market for exchanging goods from the mother-city for raw materials obtained from the natives.
There were also special causes for colonisation expeditions sent out by Greek states. Miletus and the southern Ionian cities were unable to expand in Caria, as the north Ionian cities expanded into Lydia, because the Carians were too strong for them; and Lycia presented the same barrier to Rhodes.
Relation of the colony to the mother-city.
Wherever the Greek went, he "retained his customs and language" (Bradley) and made a Greek polis (city state). The colony was seen as a public enterprise and the bond of kinship with the "mother-city" was carefully fostered. The emigrants took fire from the public heath of their city to light the fire on that of their new home. Links were especially strong between the "mother city" and colony during times of religious festivals and various marks of filial respect were shown by the colony to the "mother-city".
The results of colonisation.
The transformation of Greece's economy from a primitive agricultural based economy to that of trade, industry and money as a result of colonisation, though it took three centuries.
Economic and social effects.
Agriculture.
Large expanses of fertile land were found around the shores of the Black Sea, at Cyrene in North Africa, in southern Italy and in Sicily. This encouraged the growth of grain products such as corn and wheat, which was used to feed the growing population of mainland Greece.