The Nuclear Non-Proliferation Treaty was signed in 1968 by most of the nations of the world. At the time of signing, the known nuclear powers were Russia, the United States, China, the United Kingdom, and France. Since then, India, Pakistan, North Korea, and (likely) Israel have acquired nuclear weapons. None of those four countries are part of the Nuclear Non-Proliferation Treaty. The aim of the Nuclear Non-Proliferation Treaty was to prevent new nations from acquiring nuclear weapons and to encourage those states that already had nuclear weapons to disarm.

In the years leading up to World War One, the world witnessed great advances in technology that could be used to defend and fortify positions (most notably the machine gun), but far fewer advances in technology that aided mobility and attacking. In such a situation as existed on the Western front of Europe during World War One, the advantage was firmly in the hands of those in a defensive position. This lead to a massive stalemate in which the Allied and Central powers faced off across a few miles of unmanned terrain (“No Man’s Land”), and traded suicidal attacks over the top.

Sputnik was a Soviet-built and operated satellite that was the first man-made object to orbit the Earth. The voyage of Sputnik set off alarms in the United States and began the decades-long Space Race between the United States and the Soviet Union.

Moore's Law is a law of computer engineering that states that the power of computers will double roughly every two years. Specifically, it states that the number of transistors (part of a circuit that controls the precise flow of current through circuit boards) doubles in an integrated circuit every two years. So far, Moore's Law has proved extremely prescient. 

Prior to the invention of penicillin and other antibiotics, a significant proportion of battlefield deaths occurred from diseases that we now consider preventable. Antibiotics allow doctors to treat bacterial infections very effectively. Penicillin was invented in 1928, and the difference between the number of people who died from infections in World War One compared to those who perished from the same causes in World War Two is nothing short of miraculous. Of course, penicillin has also had a massive impact on the number of people around the world who die from infectious diseases. By some estimates, penicillin has saved over a hundred million lives since its first usage in the early 1930s.

Penicillin was invented by Alexander Fleming in 1928. The story goes that Fleming was experimenting with bacterial molds when he went away on vacation; upon returning, he discovered that one of his bacterial cultures was contaminated with a fungus and that the cultures surrounding it had been destroyed. So, completely by accident, Fleming discovered one of the most important medicines in human history—the antibacterial penicillin. 

Prior to the mid-1950s, when Salk's vaccine for polio was first provided for the public to use, polio had been one of the most devastating diseases in the Western world. It affected mostly children and caused death in many cases and paralysis in many others. In 1952, America experienced the worst epidemic of polio in the nation's history as many tens of thousands of children died or were paralyzed, so when Salk announced that he had developed a completely effective vaccine for polio, he was greeted as a national hero and a miracle worker. Today, the disease has been completely eradicated in the Western world and eradication efforts have been ongoing throughout the rest of the world. It is hoped that before 2020, the disease will have been completely isolated to human history.

Marie Curie was a Polish scientist who in the first decade of the twentieth century did pioneering work on the nature of radioactivity in elemental matter. She discovered, among other things, two new elements and has received two Nobel prizes. 

The Green Revolution took place during the 1950s and 1960s and is one of the primary causes behind the rapid growth in population seen around the world since the end of the Second World War. The Green Revolution involved wholesale changes and technological innovations in the area of agriculture that have allowed farms to be far more productive and efficient than they were previously. The Green Revolution, by some estimates, is credited with allowing an additional one to two billion people to survive on Earth.

World War I ended with the capitulation of the Germans and a victory for the allied powers. The treaty was called the Treaty of Versailles, and it is very important for understanding what would happen next in the history of Europe. The treaty essentially blamed Germany for the entirety of World War I and established harsh, almost impossible, conditions and debts for the Germans to try and pay off. This led, directly, to the rise of Hitler and Nazism and the outbreak of World War II.