I should document on the threat what @anartist discussed by PM. The most likely “second world” today are countries that have industrialization, yet lag behind in standard of living: eastern Europe, some South American nations, China and India. Some of these countries are quite advanced, but are held back by a large, poor population and high birth rates. Some nations, like the oil states, may have a high GDP but it’s not distributed throughout the population.
Some of these “second world” states will always be held back as long as their governments discourage individual initiative at all levels (China and Russia prime examples), or where an elite skims off most of the wealth, leaving ordinary people with little (South America, Asia and increasingly the US).
“Who’s got the nukes” is not a major determinant factor in world power; as these things are now viewed as terror weapons. Power has now shifted back to the 19th century model of control of shipping lanes and ability to project military force anywhere in the world. Any two-bit dictatorship can have nuclear weapons now, if the leaders are willing to bankrupt the economy and risk embargo (North Korea and Iran examples). We’re back to physical protection of trade as the determinant factor of power. The US is the only nation in the world with a navy big enough to do this, for now. Of course the US is in the position the UK was 100 years ago, king of the hill but can’t afford to maintain that power.
I should clarify that nuclear weapons are only terrorist devices as long as some power (like the US) maintains a large stockpile of them, the ability to deliver them anywhere and the determination to use them against any rogue nation that dares use them. If the “big stick” is abandoned, all bets are off.
In terms of economic power, the world is divided into three: those that have a high standard of living, those that are headed there and those going nowhere. The old terminology of “First, second and third worlds” in their original meanings, died with the breakup of the Soviet Union and Warsaw Pact.