The terms developed nation and undeveloped nation have come into favor in recent years to describe nations. The terms 1st world country, 2nd world country and 3rd world country are outdated terms that refer to the USA and its allies as capitalist 1st world countries; communist countries like Soviet Russia, China and its allies as 2nd world countries; and everyone else as a 3rd world country. The term has also been circulated to mean Christian countries meaning the USA and its allies, as 1st world countries; atheist countries meaning Russia and China, as second world countries; and everyone else as a 3rd world country. Wikipedia has a political map of what the world looked like in 1975 when these terms where in common use. History.com has a quick overview of 1st, 2nd and 3rd world countries as it relates to capitalism and communism and so does NPR.
Today, these maps make little sense. Mexico is now part of the 1st world because of NAFTA and the new USMCA treaty, many “communist” countries are no longer communist and some of the USA’s “allies” take vocal stands against the USA due to its biased support of Israel in violation of its own 1st amendment to its constitution. Finland, Sweden and India were also considered 3rd World Countries when those terms were in common use. Today India has a multi-billion dollar IT Industry while Finland and Sweden are known for their robust, world class banking systems. Much of Europe is now atheist, especially among younger people and many European economies have a mesh of capitalist, free market and socialist economies. California, a province of the United States is big on socialist policies and socialism is very similar to communism.
In terms of both economic trade and humanitarian aid, the terms developed nation and undeveloped nation are more appropriate and the terms can be used within a nation as well to describe different stages of development within the nation, for example using the term “the undeveloped part of town”. Many people are actually advocating for a category based system where nations are assigned points for infrastructure, democracy, religious freedom, economic opportunity, human rights compliance and social security. The resulting system would yield nations that are Tier 1, Tier 2, Tier 3, Tier 4 or Tier 5 developed. In the mean time, nations are referred to most commonly as developed and not developed based on economic opportunity and freedom from religious oppression.
In addition to these two primary factors, undeveloped nations are mostly concerned with food security, access to clean water, waste sanitation and building basic infrastructure. In contrast developed nations focus primarily on creating economic opportunities for everyone, technology innovation, international treaties and are often defined by having a major metropolitan area like New York, Los Angeles, Paris, London, Tokyo, Singapore, Beijing, Dubai or São Paulo. Strictly having a large metropolitan area does not necessarily make a nation developed. For example if there is a lack of economic opportunity and the metropolitan area is not engaged in global sustainability goals, it would not necessarily qualify as a developed nation and that is where the tiered system would come in. Similarly, not having a metropolitan area with a population over 1 million people does not necessarily define the nation as underdeveloped. Having a nation that is not overcrowded and polluted is a definite sign of a developed nation.