- [Narrator] Plague is
notorious for causing
mass sickness and devastation.
But as much tragedy as
the disease has caused,
it also helped drive crucial
scientific and social progress.
Plague is an infectious disease
caused by the bacterium Yersinia pestis.
It mainly affects rodents,
and spreads by way of insects.
Because of these insect carriers,
plague has been passed onto humans
with devastating consequences.
Three major plague pandemics
have occurred in human history.
And while they occurred centuries apart,
they shared similar traits
that paved the way for
the spread of disease.
One cause of plague pandemics
was the rise of international trade.
Trade routes connected
once-isolated communities
and created large economic networks.
But by facilitating the movement
of goods between communities,
trade routes also facilitated
the movement of germs.
International trade was an impetus
for the first plague pandemic on record,
the Plague of Justinian.
In the sixth century,
outbreaks began in Egypt
and, thanks to land and sea trade routes,
they spread throughout
the Byzantine Empire.
Named after the emperor at the time,
the Plague of Justinian is
estimated to have wiped out
about half of Europe's population.
Growing economies also
made way for urbanization
and a rising urban population.
This resulted in crowded neighborhoods
and the accumulation of waste,
which created unsanitary
living conditions.
Cities and their residents
essentially became incubators
for germs and diseases.
This was particularly
evident in the second
and most infamous plague pandemic.
In the 14th century,
Europe was experiencing an
economic and population boom,
especially in cities.
Proper waste management
did not exist at the time,
making cities vulnerable to disease.
After trade routes
brought plague from Asia,
where it killed millions in
China and the Middle East,
the disease wiped out about a
third of Europe's population,
earning itself the
moniker the Black Death.
What also aided in the
transmission of the disease
was the lack of medical knowledge.
For most of human history,
the cause of illnesses,
germs, was unknown,
making sicknesses like
the plague a mystery.
This lack of knowledge
drove the spread of disease
as recently as the 19th century.
Outbreaks in northwest India
eventually reached major
port cities in China.
In just over a century,
plague was exported throughout the globe
and caused outbreaks in every
continent except Antarctica,
making it the most widespread
pandemic in history.
This plague pandemic,
however, was the last.
In 1894, scientists
discovered the bacteria
behind the plague outbreaks.
Their discovery helped further
developments in microbiology,
medicine, urban planning,
and sanitation methods,
which led to the treatment
and prevention of the disease.
Economic expansion, urbanization,
and a lack of medical knowledge
contributed to the
disastrous spread of plague.
In turn, however, the
disease helped catapult
crucial advancements in
science and public health,
very well making plague
pandemics a thing of the past.
