Salt's ability to preserve foo was a foundation of civilization. It eliminated the dependence on the seasonal availability of food and it allowed travel over long distances. It was also a desirable food seasoning. However, salt was difficult to obtain, and so it was a highly valued trade item, which followed the pull of economics along salt roads, some of which had been established in the Bronze age. Until the twentieth century, salt was one of the prime movers of national economies and wars.