1900 C.E. to Present - AP World History: Modern

Haile Selassie was the Emperor of Ethiopia from 1930 to 1974. He is notable for his defense of Ethiopia against Mussolini's Italian invasion and for modernizing Ethiopia into the twentieth century.

The Russian legislature was called the Duma. It was created by the Tsar to give in to calls for democracy, but in reality, it had limited powers to effect legislation.

1931 could reasonably be seen as the beginning of World War Two in East Asia. This was the year when Japan invaded mainland China, occupying the territory of Manchuria and insituting a puppet-government that lasted until the end of the war in 1945.

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.

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.

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.

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.

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.

Mutually Assured Destruction (M.A.D.) is the belief that two nuclear powers will not launch a nuclear attack on one another because such an attack would ensure the complete annihilation of both the initial attacker and the defender. Essentially, each country can thought to be saying, "If you nuke me, I will nuke you back." This concept acted as a deterrent during the Cold War between the United States and the Soviet Union.

The full list of countries who possessed nuclear weapons in 2014, in the order they acquired them, reads as follows: The United States (1945), Russia (1949), The United Kingdom (1952), France (1960), China (1964), India (1974), Pakistan (1998), North Korea (suspected 2006), Israel (unknown).

To date, the United States is the only country known to have used nuclear weapons in a conflict, dropping two bombs on the Japanese cities of Nagasaki and Hiroshima at the end of the Second World War.

The Nuclear Non-Proliferation Treaty was signed to prevent the spread of nuclear weapons to nations that had not already acquired them and to encourage disarmament among those nations that already possessed nuclear weapons. India, Pakistan, and Israel have never signed the treaty, but North Korea originally signed the treaty before announcing its withdrawal in 2003. North Korea is thought to have developed nuclear weapons by 2006, making it the only state to withdraw from the Nuclear Non-Proliferation Treaty and then acquire nuclear weapons.

The Nuclear Non-Proliferation Treaty was signed in 1968. Its primary purpose was to prevent new nations from acquiring nuclear weapons; however, another part of the treaty was to encourage those nations that already had nuclear weapons to disarm. This has been largely unsuccessful, although every nation that signed the treaty has reduced its supply of nuclear weapons.

The Archduke of Austria-Hungary, Franz Ferdinand, was assassinated in June of 1914 by Gavrilo Princip. After his assassination the Austrian Empire implicated much of the Serbian high command and used the incident as a pretext to invade Serbia. This action disturbed the entangled alliances of Europe and lead directly to the outbreak of World War I a few months later.

During World War One German U-boats were actively engaged in preventing the British and French from receiving reinforcements and economic assistance from America and the rest of the Western Hemisphere. The most well-known incident occurred in 1915 when a German U-boat sank an American passenger ship called the Lusitania and killed some 200 American civilians in the process. The action was widely condemned, but it never directly lead to a German suspension of its unrestricted submarine warfare. Instead its primary consequence was to help encourage American and Brazilian public opinion to turn in favor of aiding the allies in the Great War.

The technology for guided missiles developed after World War I, but everything else was a part of warfare from World War I on, and some, like the machine gun, had already been used in earlier conflicts. This was the first war that involved the use of aircraft for fighting that also saw the use of poisonous gases (like mustard gas) and tanks.