It’s a graph of regional GDP per capita as a percentage of the U.S. Latin America was around 40% around 1950, but has declined to around 25% by 2018. Sub-saharan africa has slowly lost ground since 1950. Southeast asia has gone from almost as poor as Africa in 1950 to almost as rich as southern europe (50% of US GDP per capita).
What makes some countries rich and some countries poor? In the modern era, I think political dysfunction explains a lot. Developing countries with neoliberal governments that started out authoritarian (Singapore, Korea, Taiwan) have done well. Countries that can’t maintain a stable government have suffered.
In my home country, they were experiencing 5-6% per capita GDP growth for about 15 years. But then a motley coalition of idealistic students and Islamists overthrew the government. I suspect that will lead to a lengthy period of slow growth, because who wants to invest in a country where people regularly overthrow the government?