The twenty years of war in the middle of the century had a dramatic effect. Grain exports through Gdańsk in the early 1600s averaged 200,000 tonnes per annum, reaching some 250,000 tonnes in the bumper year of 1618. The figure for 1651, after three years of Cossack unrest, was only 100,000 and two years later this had fallen to 60,000, which remained the average yearly figure for the rest of the century. The import of colonial goods through Gdańsk went up by 10 per cent between 1615 and 1635, and then shot up by 50 per cent between 1635 and 1690. Only in the case of Gdańsk are such comprehensive figures available, and it is impossible to ascertain the position for other ports like Elbląg, or for overland trade with Germany and Muscovy, where the balance was more favourable. The wars also had a catastrophic effect on the export of cattle and horses reared in the south-eastern areas of the Commonwealth.
The mid-century wars were disastrous in other respects. The casualties were not in themselves remarkable, except in the southeastern areas. The Tatars led many thousands off into slavery and Tsar Alexey deported large numbers to colonise newly conquered areas of Siberia, but the most destructive invaders were the Swedes. The wholesale razing of crops, the burning of villages and towns, and the removal of cattle brought about famine, compounded by plague. The results were devastating. Between 1600, when the population of the Commonwealth stood at over ten million, and 1650 there had been an increase of 23 per cent, but in the ten years between 1650 and 1660, it fell by at least a quarter, to below the original ten million mark. Population density in the Polish heartlands of Wielkopolska, Małopolska and Mazovia had reached 26.3 per square kilometre by 1650, but by 1660 it was down to 19.9. With war and famine destroying their villages, people wandered the countryside in search of less badly affected areas. Food production fell to disastrous levels. By 1668, when the situation had stabilised, 58 per cent of arable land on szlachta estates was lying fallow, while the figures for Church estates and royal lands were 82 and 86 per cent respectively.
The greatest casualties were the towns. At the beginning of the century, Gdańsk was still by far the largest, with 70,000 inhabit—ants, followed by Warsaw (30,000), Kraków (28,000), Poznań and Lwów (20,000), Elbląg (18,000), Toruń (12,000) and Lublin (10,000). Of the other nine hundred or so townships throughout the Commonwealth, most had between five hundred and 2,000 inhabitants. In all, about a quarter of the population lived in towns. The Swedish army looted and torched the towns it entered, with the result that between 1650 and 1660 the urban population of the Commonwealth declined by up to 80 per cent.
The major towns had long been under pressure from private towns belonging to magnates or the Church, losing much of their business as agents for the produce of the country and as providers of finished goods to the locality. They were poorly represented and heavily taxed. After the wars, which destroyed much of Warsaw, Kraków, Poznań, Lublin and Wilno—the latter was put to fire and sword for seventeen days by Alexey in 1655—they found it difficult to rebuild. Such investment as was forthcoming was lavished on the private towns by their solicitous owners. But these private towns could not replace the older ones in one crucial respect. They were functionally limited to the exploitation and the provision of essentials to a given area, and there was little scope for enterprise or investment by individual merchants or manufacturers. They never grew into centres of finance and credit which could generate their own wealth and industry, yet the older towns were in no position to carry on this function as before. Only the magnates, the Church and the crown were capable of promoting industrial development, but they were neither motivated nor equipped for the job.
Elective monarchs tended to regard the Commonwealth not as part of their patrimony, to be cared for and enriched on behalf of their descendants, but rather as a sinecure to be enjoyed and a means to enhance their own glory or further the cause of their dynasty. It was only when it had become clear to Zygmunt III that his son would succeed him that he began to care for the economy of the Commonwealth. In 1624 he set up new steelworks at Bobra and Samsonów, and a few years later modernised the royal mines. Władysław IV, who felt dynastically attached to Poland, took an active part in its industrial development, but even where the will existed, the means often did not, as the Commonwealth did not have a proper fiscal regime in place.