Southern Iraq during Akkadian period seems to have been approaching its modern rainfall level of less than per year, with the result that agriculture was totally dependent upon irrigation. Before the Akkadian period, the progressive salinisation of the soils, produced by poorly drained irrigation, had been reducing yields of wheat in the southern part of the country, leading to the conversion to more salt-tolerant barley growing. Urban populations there had peaked already by 2,600 BC, and demographic pressures were high, contributing to the rise of militarism apparent immediately before the Akkadian period (as seen in the Stele of the Vultures of Eannatum). Warfare between city states had led to a population decline, from which Akkad provided a temporary respite. It was this high degree of agricultural productivity in the south that enabled the growth of the highest population densities in the world at this time, giving Akkad its military advantage.