As countries develop their citizens live longer, healthier lives and have more access to education, healthcare and jobs. This helps people lead more productive and fulfilling lives and also makes it easier for families to meet their basic needs. Developing countries also tend to be more stable, which encourages investment and trade. Having more wealth also increases the power of a country in world affairs as it allows them to build stronger relationships with other countries and be less likely to be interfered with by outside forces.
Another reason why developing nations are important is that they reduce inequality. Inequality is a major problem for countries and breads resentment, conflict and even armed violence. As a country becomes more developed, it becomes less unequal and this is a good thing for everyone as it shows that the government is doing well for its citizens.
Researchers have been working on developing theories of human development and have found that there are many factors that influence it. For example, researchers have found that culture is an important factor in human development and that different cultures have different approaches to human development. It is still not clear how much of human development is caused by nature and how much is influenced by nurture but this research is ongoing.