What is a flu? 
Influenza or flu is a virus that attacks the respiratory system. The flu virus is highly contagious: When an infected person coughs, sneezes or talks, respiratory droplets are generated and transmitted into the air, and can then can be inhaled by anyone nearby. Additionally, a person who touches something with the virus on it and then touches his or her mouth, eyes or nose can become infected.
What caused the Spanish flu?
It’s unknown exactly where the particular strain of influenza that caused the pandemic came from; however, the 1918 flu was first observed in Europe, America and areas of Asia before spreading to almost every other part of the planet within a matter of months. Despite the fact that the 1918 flu wasn’t isolated to one place, it became known around the world as the Spanish flu, as Spain was hit hard by the disease and was not subject to the wartime news blackouts that affected other European countries. (Even Spain's king, Alfonso XIII, reportedly contracted the flu.) One unusual aspect of the 1918 flu was that it struck down many previously healthy, young people—a group normally resistant to this type of infectious illness—including a number of world war I servicemen.
In fact, more U.S. soldiers died from the 1918 flu than were killed in battle during the war. Forty percent of the U.S. Navy was hit with the flu, while 36 percent of the Army became ill, and troops moving around the world in crowded ships and trains helped to spread the killer virus. Although the death toll attributed to the Spanish flu is often estimated at 20 million to 50 million victims’ worldwide, other estimates run as high—around 3 percent of the worlds population. The exact numbers are impossible to know due to a lack of medical record-keeping in many places.
Origination of the Spanish flu
The Spanish Flu did not originate in Spain, though news coverage of it did. During world war I,Spain was a neutral country with a free media that covered the outbreak from reporting on it in Madrid in late may of 1918. Meanwhile,Allied countries and the central powers had a wartime censors who covered up the news of the news to keep morale high.[the Spanish meanwhile , believed the virus came from France and called it "french flu"]. 

Finding cure to the flu
When the 1918 flu hit, doctors and scientists were unsure what caused it or how to treat it. Unlike today, there were no effective vaccines or antiviral, drugs that treat the flu. (The first licensed flu vaccine appeared in America in the 1940s. By the following decade, vaccine manufacturers could routinely produce vaccines that would help control and prevent future pandemics.) Complicating matters was the fact that World War I had left parts of America with a shortage of physicians and other health workers. And of the available medical personnel in the U.S., many came down with the flu themselves.
Additionally, hospitals in some areas were so overloaded with flu patients that schools, private homes and other buildings had to be converted into makeshift hospitals, some of which were staffed by medical students.Officials in some communities imposed quarantines, ordered citizens to wear masks and shut down public places, including schools, churches and theaters. People were advised to avoid shaking hands and to stay indoors, libraries put a halt on lending books and regulations were passed banning spitting.
According to The New York Times, during the pandemic, Boy Scouts in NEW YORK City approached people they’d seen spitting on the street and gave them cards that read: “You are in violation of the Sanitary Code.”

How the flu came to an end
By the summer of 1919, the flu pandemic came to an end, as those that were infected either died or developed immunity. Almost 90 years later, in 2008, researchers announced they’d discovered what made the 1918 flu so deadly: A group of three genes enabled the virus to weaken a victim’s bronchial tubes and lungs and clear the way for bacterial pneumonia.
Since 1918, there have been several other influenza pandemics, although none as deadly. A flu pandemic from 1957 to 1958 killed around 2 million people worldwide, including some 70,000 people in the United States, and a pandemic from 1968 to 1969 killed approximately 1 million people, including some 34,000 Americans.