There are enormous gaps in development between rich and poor countries globally. Wealthy nations have moved to service economies while some poorer states remain subsistence-based. Several metrics are used to measure development, including GNP, GDP, and GNI which measure total output, as well as factors like productivity, infrastructure, and health outcomes. However, these metrics do not account for inequality within countries or informal economies. Development theories offer different perspectives on why disparities exist, with modernization models arguing countries follow similar development paths, while dependency and world systems theories see structural relationships limiting poorer regions' development.