Measuring a country's development is a complex task. The United Nations' Human Development Index, or HDI, is one of the most trusted snapshots of national progress, and takes into account more than 150 indicators from over 150 countries. It then boils them down into a single score.
Every country lands somewhere between zero and one, with one marking the best possible outcome and zero the worst. The UN then sorts nations into four tiers: low human development (below 0.55), medium (0.55 to 0.70), high (0.70 to 0.80), and very high (0.80 and above).
The 30 countries below all sit in that lowest tier, and each has its own story of how it got there. Click on to discover which countries are on the list and why.