Northern coast of the Black Sea. In this way Poland became a commercial country, and the merchants of her cities, particularly those of Cracow, were famous for their wealth. With the conquest of Constantinople and the Black Sea by the Turks, those continental routes were cut and the trade of Poland was ruined. The cities, which had been rapidly gaining political power, lost it very soon. At the same time the great geographical discoveries then made opened up new sea-routes and gave a strong impetus to the commerce of the Western sea-faring nations. This commercial growth, and the industrial development of England and Flanders, produced a rapid increase in the population of the countries of North-western Europe, which became a great market for Polish grain. Thus Poland, having lost her commercial importance, gained very favourable conditions for agricultural development. The fifteenth century is in Poland a period when agriculture and landed property are organised on a large scale. Till that time she was a country of small husbandry intended only for local consumption. With the opening of foreign markets, large agricultural units were rapidly formed by means of clearing the forests, of internal colonisation, of the amalgamation of small units and of expansion towards the South-East to the fertile territories of the ancient Grand Duchy of Kiev, which had been depopulated in the twelfth and thirteenth centuries by the nomads of the Steppes, and which, under the protection of Poland's military power, were now again colonised. All this work was done by the Polish gentry, which, availing itself of its newly-won political power, grasped the entire profit made possible
