The term "Third World" is no longer applicable
The categories "first world", "second world" and "third world" were never categories of economic development. They were categories of political allegiance during the cold war with:
- First world: The "Free World": United States, other NATO members and countries aligned with them.
- Second world: The "Communist World": The Soviet Union, its satellite states, other Warsaw Pact members, China, and countries aligned with them.
- Third world: Countries unaligned with either power-block.
While this political division made a lot of sense in the second half of the 20th century, it is no longer a useful model to describe geopolitical allegiances in the 21st century.
However, due to the tendency of third world countries of having a lower level of economic development than most 1st and 2nd world countries, the term "Third World" became synonymous with poor and economically underdeveloped countries and is still sometimes used that way.
What term you actually mean
The categories used by political scientists to group countries by economic development level, are:
- Developed countries (United States, Canada, most parts of Europe, Australia, Japan...)
- Developing countries (Russia, India, China, Brazil...)
- Least Developed countries (Somalia, Rwanda, Afghanistan, Haiti...)
But how do you put countries into these categories objectively? While there is no one objective rating system, one option is the Human Development Index. It rates countries by:
- Quality of health, measured in life expectancy at birth
- Education level, measured in average years spent in school education.
- Standard of living, measured in Gross National Income per capita.
This system isn't perfect. For example, it doesn't take inequalities into account. It also uses measurements which represent quantity but not quality. But when you are looking for a way to compare ~200 countries in the world with ~7.8 billion inhabitants in an objective manner, you have to apply some simplifications.
How does the US measure in these criteria?
Life expectancy at birth: Slight fluctuations, but basically the same since 10 years ago: 78.8 years. World average in 2014 was 72.2.
Years spent in education: 16.5, which ranks it as 8th in the world. Higher education becoming less and less affordable in the US is a problem, but so far it does not lead to less people going to college.
Gross Domestic Product per capita: 10th highest in the world. It is raising steadily for decades, but so does the GDP per capita of most other countries. 2020 might actually see a decline due to the COVID-19 pandemic. But the same applies to the rest of the world (although the US is the developed country which currently gets hit the hardest, but the short-term and long-term effects on the US GDP are still very much speculation).