Why Greeks left their country?

Answer 1

Principally because of over-population. With small farms, unirrigated in poor country, it was not possible to subdivide them amongst several sons, so a city-state had to try to take land from neighbouring cities. This fighting might reduce also the male population somewhat, but the limited overall supply of land and human fecundity meant that eventually they had to send off the surplus to new areas to seize land and establish new cities. This resulted in the growth of Greek cities around the coast of the Mediterranean and Black Seas. Another reason was to get rid of non-propertied people living in the cities. These were potentially trouble-makers, and sending them off allowed tham to be raised to property owners in the new site. As a side benefit, establishing a colony allowed political opponents to be shipped off too.