this period to see this phenomenon as an "Uruk expansion". This has been reinforced by the political situation in the modern Near East and the impossibility of excavating in Mesopotamia. Recent excavations have focused on sites outside Mesopotamia, as a 'periphery', and with an interest in how they related to the 'centre', which is paradoxically the region in this period which is least well-known—limited to the impressionistic discoveries of the monuments of Uruk. Subsequently, theories and knowledge have developed to the point of general models, drawing on parallels from other places and periods, which has posed some problems in terms of getting the models and parallels to fit the facts revealed by excavations. Guillermo Algaze adopted the World-systems theory of Immanuel Wallerstein and theories of international trade, elaborating the first model that sought to explain the Uruk civilization. In his view, which has met with some approval, but has also found many critics, the 'Urukians' created a collection of colonies outside Lower Mesopotamia, first in Upper Mesopotamia (Habuba Kabira and Jebel Aruda, as well as Nineveh, Tell Brak and Samsat to the north), then in Susiana and the Iranian plateau. For Algaze, the motivation of this activity is considered to be a form of economic imperialism: the elites of southern Mesopotamia wanted to obtain the numerous raw materials which were not available in the Tigris and Euphrates floodplains, and founded their colonies on nodal points which controlled a vast commercial network (although it remains impossible to determine what exactly was exchanged), settling them with refugees as in some models of Greek colonisation. The relations established between Lower Mesopotamia and the neighbouring regions were thus of an asymmetric kind. The inhabitants of Lower Mesopotamia had the advantage in the interactions with neighbouring regions as a result of the high productivity of their lands, which had allowed their region to "take off" (he speaks of "the Sumerian takeoff") resulting in both a comparative advantage and a competitive advantage. They had the most developed state structures and were thus able to develop long-distance commercial links, exercise influence over their neighbours, and perhaps engage in military conquest. Algaze's theory, like other alternative models, has been criticised, particularly because a solid model remains difficult to demonstrate while the Uruk civilization remains poorly known in Lower Mesopotamia aside from the two monumental complexes that have been excavated at Uruk itself. We are therefore poorly placed to