For the past couple of weeks Americans have been inundated with information on a new global fear: chemical weapons. While during the Bush years we heard everything under the sun about the catch-all WMDs, or “weapons of mass destruction,” Americans are relatively uninformed about chemical weapons. Evidence suggesting Syrian president Bashar Assad used sarin gas, a deadly nerve agent, against his own people over the course of the Syrian civil war has led the United States to the brink of military engagement.

In a Senate Foreign Relations Committee hearing yesterday, Secretary of State John Kerry made the erroneous statement, “In the nearly 100 years since this global commitment against chemical weapons was made, only two tyrants have dared to cross the world’s brightest line. Bashar al-Assad has now become the third.”

The reality though, is that since the Geneva Protocol became international law in 1925, following the deaths of over 100,000 people in World War I through the use of chemical weapons such as mustard gas, there have been six world leaders who have made the decision to use these deadly weapons. Here’s a look.

1. Benito Mussolini, 1934

When Italy’s fascist dictator made the misguided decision to invade Ethiopia in an effort to build an Italian empire, he also made the mistake of violating the less than ten year old Geneva Protocol. Specifically, Mussolini dropped mustard bombs on Ethiopian civilians. Ethiopian emperor Hailie Selassie reported to the League of Nations that tens of thousands of individuals were killed as a result.

2. Emperor Hirohito, 1937 – 1939

During the Japanese imperial invasion of China at the start of the Second Sino-Japanese War, Emperor Hirohito regularly dropped mustard gas during battles to aid in the invasion of Chinese cities.  The Japanese military also used bacteriological weapons, by dropping bombs containing bubonic plague carrying fleas.  While there is no official death toll for the chemical attacks, over 300,000 died during the course of the conflict.

3 Adolf Hitler 1940-1945

While Hitler never used chemical weapons on the battlefield during World War II, he still definitely violated international laws by killing millions of Jews in concentration camps through the use of gas chambers. Specifically, the gas chambers used a chemical agent known as Zyklon B, which contains hydrogen cyanide and prussic acid, which are banned by the Geneva Protocol.

4. Gama Abdul Nasser 1963-1967

The president of Egypt ordered the use of chemical weapons during the North Yemen civil war. Egypt supported the republicans, who were attempting to oust the royalist regime via a coup d’etat. Nasser provided 70,000 troops as well a chemical weapons, a fact he vehemently denied. After the conflict, the International Red Cross confirmed that chemical weapons had been used through forensic evidence, suggesting chemical weapons caused roughly 1,500 fatalities.

5. Saddam Hussein 1978-1991

During the Iraq-Iran War, Saddam Hussein used chemical weapons extensively to gain territory in Iran, specifically the nerve agents tabun and sarin. Later, during the Persian Gulf War, Hussein again used chemical weapons, particularly mustard gas, against the Kurdish and Shiite Muslim populations in the northern areas of Iraq. This directly lead to U.S. involvement in the conflict. It’s estimated that the total number of causalities from chemical weapons in these conflicts are in the tens of thousands.

6. Bashar al-Assad 2012-2013

In December of 2012 unconfirmed reports started trickling out of Syria that Bashar Assad had used sarin nerve gas against rebel and civilian populations. On August 21, 2013, the United States confirmed that the Assad regime had launched a chemical weapon attack that caused the deaths of nearly 1,500.