The term LICs in the passage most likely represents

Gordon Childe used the term urban revolution to describe the change in society marked by the emergence of the first cities some 5500 years ago. The areas that first witnessed this profound social and economic change were Mesopotamia, the valleys of the Tigris and Euphrates rivers, the lower Nile valley and the plains of the river Indus. Later, urban civilisations developed around the Mediterranean, in the Yellow River valley of China, in South East Asia and in the Americas. Thus the first cities mainly emerged in areas that are now considered to be LICs. The catalyst for this period of rapid change was the Neolithic Revolution, which occurred about 8000 BCE. This was when sedentary agriculture, based on the domestication of animals and cereal farming, steadily replaced a nomadic way of life. As farming advanced, irrigation techniques were developed. Other major advances that followed were the ox-drawn plough, the wheeled cart, the sailing boat and metallurgy. However, arguably the most important development was the invention of writing in about 4000 BCE, for it was in the millennium after this that some of the villages on the alluvial plains between the Tigris and Euphrates rivers increased in size and changed in function so as to merit the classification of urban. Considerably later than the first cities, trading centres began to develop. The Minoan civilisation cities of Knossos and Phaistos, which flourished in Crete during the first half of the second millennium BCE, derived their wealth from maritime trade. Next it was the turn of the Greeks and then the Romans to develop urban and trading systems on a scale larger than ever before.