Except for the provinces of Scania, Blekinge and Halland in the south-west of the Scandinavian peninsula, which were parts of the Kingdom of Denmark during this time, feudalism never developed in Sweden as it did in the rest of Europe. The peasantry, therefore, remained largely a class of free farmers throughout most of Swedish history. Slavery (also called thralldom) was not common in Sweden, and what slavery there was tended to be driven out of existence thanks to the spread of Christianity as well as to the difficulty to obtain slaves from the lands east of the Baltic Sea, and by the development of cities before the 16th century. Indeed, both slavery and serfdom were abolished altogether by a decree of King Magnus IV in 1335. Former slaves tended to be absorbed into the peasantry, and some became labourers in the towns. Still, Sweden remained a poor and economically backward country in which barter was the primary means of exchange. For instance, the farmers of the province of Dalsland would transport their butter to the mining districts of Sweden and exchange it there for iron, which they would then take to the coast and trade for fish, which they consumed, while the iron would be shipped abroad.