The development of agriculture is frequently seen as one of the major economic, social, and demographic thresholds in human history. From the perspective of the modern world it is often seen as an inevitable, desirable subsistence strategy, allowing larger populations, settled life, and the development of cities. Likewise it has even been argued that long-term human survival in tropical forests must have been impossible without some form of agricultural system, with agriculture developing as a result of climatic or environmental instability.