7 plagues that changed history: with Ebola's re-emergence in West Africa, a look at past epidemics that left their mark on the world.

• Author: Barnard, Bryn
• Position: TIMES PAST

What does yellow fever have to do with the size of the United States? How did tuberculosis popularize being thin?

Why did the bubonic plague contribute to Islam's rise?

Epidemics--like the Ebola outbreak in West Africa--can deal devastating blows to a society, often at breakneck speeds. But sometimes their effects go way beyond immediate suffering. Epidemics, in fact, can change the course of history.

Here are seven epidemics that wreaked havoc when they happened and changed the world in ways still felt today.

1 Bubonic Plague

The Rise of Islam

In the mid-seventh century, Muslim armies swept out of the Arabian Peninsula, crushed some of that era's greatest powers, and within decades created the biggest empire of its day. How? With lots of help from the bubonic plague, caused by the bacterium yersinia pestis.

The symptoms of the plague are fever, vomiting, and buboes--swollen and painful lymph nodes that fill up with pus. Most victims died within a week.

The plague hit Europe in two distinct pandemics, each with multiple waves: Justinian's Plague (541-42), named for the Byzantine emperor, was part of the first pandemic; the "Black Death" (1346-51) was part of the second, which finally burned out in the 1750s. (It's long been thought that the Black Death was spread primarily by rats and fleas; but new research suggests the disease was airborne, transmitted from person to person by coughing.)

The first pandemic killed 30 million to 100 million people, up to half the world's population at the time. It decimated the Byzantine and Persian Empires, claiming peasant farmers, aristocrats, and soldiers alike. And it weakened the empires' militaries, ruined their economies, and tore their social fabric to shreds, enabling the Muslim conquest of Persia (modern-day Iran), which took place from 633-51.

About 800 years after the first pandemic, the Black Death ravaged Europe, killing up to a third of its population. The badly weakened Byzantine Empire held on through the devastation but finally succumbed in 1453, when a Muslim army, led by 21-year-old sultan Mehmed, conquered Constantinople (today Istanbul, in Turkey). The plagues led to the end of Christian domination of the Mediterranean and the beginning of Islam as a global force.

2 Smallpox

The Birth of the U.S.

Would there be a United States without smallpox? Probably not.

Of all the horrific diseases that Europeans inadvertently exported on their colonizing expeditions--plague, chicken pox, cholera, diphtheria, influenza, measles, scarlet fever, typhus, tuberculosis, and whooping cough--smallpox proved the most deadly for native populations in the Americas. Caused by the variola virus, smallpox symptoms include fever, rash, headache, and masses of painful pus-filled bumps called pustules on the skin, eyes, throat, and internal organs. It was probably brought to the Americas by the Spanish in the 1520s, and within a few generations killed an estimated 20 million native inhabitants. In the Puritan northeast, many viewed the epidemics as part of God's plan. John Winthrop, the governor of the Massachusetts Bay Colony, wrote in 1634, "for the natives, they are all near dead of smallpox, so the Lord hath cleared our title to what we possess."

3 Yellow Fever

U.S. Expansion

If not for yellow fever, the United States might be a third of its current size. The deadly viral mosquito-borne illness causes fever, black vomit, and jaundice (yellowing of the skin and eyes).

In 1802, France's Emperor Napoleon Bonaparte sent a massive fleet to Haiti, (1) his most important colony in the New World, to quell a slave rebellion that began there in 1791. But nearly all the 50,000 troops he'd sent were wiped out by yellow fever.

Napoleon had envisioned the Louisiana Territory as a giant farm to feed Haiti, whose slaves, sugar, and coffee were highly profitable for France. But defeated by yellow fever, Napoleon withdrew from Haiti and in 1803 sold France's claim to the...