This is likely the test of god to us because sometimes a lot of things are very mysterious and we don't know the reasons. Reviewing back the previous pandemic, it is found that pandemic happened once every 100 years. Coincidentally, 2020 is the fourth time in history that the pandemic occurred 100 years apart. Now let us review how terrible these pandemics were!

1720 - Great Plague of Marseille/ Bubonic Plague

This pandemic was the strongest outbreak in Europe in the early 18th century. The bubonic plague that broke out in Marseille, France in 1720, killed approximately 100,000 people in and around the city. The pathogen of this plague was Yersinia pestis. At that time, a merchant ship, called Grand-Saint-Antoine, sailed from Tripoli, Cyprus (there was an outbreak of the plague at that time), and Lebanon and it finally arrived at Marseille. Several people died on board, including a Turkish passenger, a doctor and other crew members. The ship was isolated by the port authorities when it arrived at Marseille. However, isolation measures were cancelled due to the trade monopoly between Marseille and the Levant, the import of Middle East's goods, as well as the need of the Marseille's wealthy merchant to get shipment silk and cotton goods for sale at the fair. 

Just a few days later, bubonic plague broke out in Marseille. The city's hospitals were quickly filled with patients. The public also drove the plague-infected patients away from home and the city. Dead bodies were buried in the mass graves. However, the graves were also filled in a short time and thousands of corpses have piled up around the city. To prevent the spread of the plague, France promptly ordered the isolation of Marseille and other provinces. Anyone who violated the order must be executed. The authorities also established a Mur de la Peste on the outskirts of the city. In two years, out of the 90,000 residents in Marseille, 50,000 of them were killed. The plague spread north to Aix en Provence, Arles and Toulon, has caused 50,000 people died.

1820 - Cholera 

Cholera is an infection of the small intestine caused by Vibrio cholera strains. In 1820, the world's first cholera happened and it is known as "Asian cholera". The cholera pandemic began near Kolkata, India in 1817. It spread to Thailand, Indonesia, Philippines, China, Japan, and West Asia such as Oman, Iraq, and Syria due to trade and military factors. This pandemic affected almost entire Asia for 7 years until 1824. The overall death toll from cholera has not been estimated so far. However, according to records, cholera had killed at least 120000 people in Java alone at that time. 

Since 1961, cholera has spread to more than 140 countries and the number of reported cases has reached 4 million. The number of cases may be much more than that. However, in recent years, cholera has been greatly reduced. This might be due to the improvement of public cleanliness and the availability of clean drinking water.

1920 - Spanish Flu

Spanish flu originated in the United States and was the second most deadly infectious disease in human history. 8 million people in Spain, including the King of Spain, were infected with the disease. This is the reason how the outbreak of the flu gets its name.

The Spanish flu killed 25 million to 50 million people in just six months, which is more than the number of deaths during World War I (from 28 July 1914 to 11 November 1918, aka 52 months). The Spanish flu was also one of the reasons for the early end of World War I, as countries no longer had extra troops to fight. The Spanish flu can be divided into three waves. The first wave was just ordinary influenza which occurred in the spring of 1918. The second wave had the highest mortality rate and it occurred in the fall of 1918. The last wave occurred in 1919 Winter to spring 1920. In total, it had infected about 500 million people worldwide from 1918 to 1919. 

2020 - COVID-19

In 2020,  the world is facing another deadly pandemic which originated from Wuhan, China. More than 400 major cities of the world are affected by this pandemic. Italy and Iran now have the highest number of confirmed diagnoses and deaths. More than half of the world population is forced to be quarantined. The direct communication system is collapsed from person to person. Industries such as tourism, manufacturing and others have been affected severely by this pandemic. 

In addition to the four pandemics that happened just 100 years apart, there are other pandemics occurred in history, many of which are related to animals, such as influenza, tuberculosis, plague, pneumonia, SARS, H1N1 influenza, MERS, and others.