Short answers, pulled from the story.
Alfred Sauvy published an article in 1952 introducing the concept. The French demographer drew inspiration from pre-revolutionary France to define three estates. He compared capitalist nations to the first estate, communist states to the second estate, and all remaining countries formed what he called the Third World.
First World countries displayed economic prosperity during the mid-twentieth century. Technological advancement marked their societies while political stability remained common across these nations. These nations functioned as part of the Western Bloc under American leadership after NATO formed in 1949.
The Soviet Union dissolved in 1991 after decades of tension. Eastern Bloc organizations ceased functioning immediately following this event and the Warsaw Pact disbanded as member states declared independence. Without the communist bloc, the Second World label lost meaning overnight.
Today many people still use the term Third World to refer to traditionally less-developed regions like Africa. Some speakers equate it with developing nations globally or apply it to areas facing economic challenges. The historical context behind the phrase remains unclear to most users who employ the expression without explanation.
NATO formed in 1949 under American leadership to protect interests across Europe. The Warsaw Pact emerged later in 1955 with Soviet direction to create opposing forces. These organizations became known as the Western Bloc and the Eastern Bloc respectively.