The spatial separation was only partial and in the Commonwealth there were no formal ghettos. Jewish residents of cities participated in the upkeep of public infrastructure, and made other contributions, including to common military defense. The weakness of central government prevented an introduction of a uniform statewide economic policy, even as feeble attempts to implement mercantilism and state protectionism (widely then practiced in Europe) were being made. The balance of trade remained negative most of the time, and the country's transit role diminished. The lack of central controls opened the Commonwealth to exploitation by more advanced economies. The monetary crisis and chaotic policy in that area, as well as Frederick II's flooding of Poland with fake Polish currency, resulted in massive devaluations and economic losses. With the townspeople increasingly employed in agriculture, where there was demand for labor, the guild crafts and manufacturing, the mainstay of the urban middle class, became reduced to a fraction of its past capacity. However, the Commonwealth was able to preserve or rebuild much of the mining, metallurgy and heavier industries, some of which were important for military applications. Nationwide the urban classes had become marginalized and lacked influence, as even by the end of the 18th century the population of town residents constituted no more than 15% of the Commonwealth total. Most cities were private, as opposed to "royal" or public, with their inhabitants accordingly subjected to arbitrary obligations imposed by feudal owners. In the 18th century royal city of Kraków, 55% of the grounds within the city walls belonged to the Church, 17% to nobility interests and only the rest to the actual city folks. The degradation of towns was recognized as one of the leading factors contributing to national decline by the more enlightened of szlachta publicists (Garczyński, Fredro, Leszczyński). The Commonwealth city populations were fragmented on the bases of trade, class, ethnicity, religious affiliation or jurisdiction type and consumed by internal conflicts. The most enterprising and successful of burghers were able to join the ranks of nobility, thus leaving the urban occupations or introducing additional tensions within cities. Townspeople in larger cities, including Danzig, supported with dedication and generosity the national cause during the foreign invasions. The Commonwealth's urban upper layer had lost its previously prominent role in the promotion of cultural advancement, but in Silesia, where Polish gentry no longer existed, Protestant townspeople continued Polish language educational and cultural activities, including literary work and publications, in several cities.