has occurred in many forms throughout the world.

But one institution stands out for both its global scale and its lasting legacy.

The Atlantic slave trade,

occurring from the late 15th to the mid 19th century

and spanning three continents,

forcibly brought more than 10 million Africans to the Americas.

The impact it would leave affected not only these slaves

and their descendants,

but the economies and histories of large parts of the world.

There had been centuries of contact between Europe and Africa

via the Mediterranean.

But the Atlantic slave trade began in the late 1400s

with Portuguese colonies in West Africa,

and Spanish settlement of the Americas shortly after.

The crops grown in the new colon ies, sugar cane, tobacco, and cotton,

were labor intensive,

and there were not enough settlers or indentured servants

to cultivate all the new land.

American Natives were enslaved, but many died from new diseases,

while others effectively resisted.

And so to meet the massive demand for labor,

the Europeans looked to Africa.

African slavery had existed for centuries in various forms.

Some slaves were indentured servants,

with a limited term and the chance to buy one's freedom.

Others were more like European serfs.

In some societies, slaves could be part of a master's family,

own land, and even rise to positions of power.

But when white captains came offering manufactured goods,

weapons, and rum for slaves,

African kings and merchants had little reason to hesitate.

They viewed the people they sold not as fellow Africans

but criminals, debtors, or prisoners of war from rival tribes.

By selling them, kings enriched their own realms,

and strengthened them against neighboring enemies.

African kingdoms prospered from the slave trade,

but meeting the European's massive demand created intense competition.

Slavery replaced other criminal sentences,

and capturing slaves became a motivation for war,

rather than its result.

To defend themselves from slave raids,

neighboring kingdoms needed European firearms,

which they also bought with slaves.

The slave trade had become an arms race,

altering societies and economies across the continent.

As for the slaves themselves, they faced unimaginable brutality.

After being marched to slave forts on the coast,

shaved to prevent lice, and branded,

they were loaded onto ships bound for the Americas.

About 20% of them would never see land again.

Most captains of the day were tight packers,

cramming as many men as possible below deck.

While the lack of sanitation caused many to die of disease,

and others were thrown overboard for being sick,

or as discipline,

the captain's ensured their profits by cutting off slave's ears

as proof of purchase.

Some captives took matters into their own hands.

Many inland Africans had never seen whites before,

and thought them to be cannibals,

constantly taking people away and returning for more.

Afraid of being eaten, or just to avoid further suffering,

they committed suicide or starved themselves,

believing that in death, their souls would return home.

Those who survived were completley dehumanized,

treated as mere cargo.

Women and children were kept above deck and abused by the crew,

while the men were made to perform dances

in order to keep them exercised and curb rebellion.

What happened to those Africans who reached the New World

and how the legacy of slavery still affects their descendants today

is fairly well known.

But what is not often discussed

is the effect that the Atlantic slave trade had on Africa's future.

Not only did the continent lose tens of millions of its able-bodied population,

but because most of the slaves taken were men,

the long-term demographic effect was even greater.

When the slave trade was finally outlawed in the Americas and Europe,

the African kingdoms whose economies it had come to dominate collapsed,

leaving them open to conquest and colonization.

And the increased competition and influx of European weapons

fueled warfare and instability that continues to this day.

The Atlantic slave trade also contributed to the development of racist ideology.

Most African slavery had no deeper reason than legal punishment

or intertribal warfare,

but the Europeans who preached a universal religion,

and who had long ago outlawed enslaving fellow Christians,

needed justification for a practice

so obviously at odds with their ideals of equality.

So they claimed that Africans were biologically inferior

and destined to be slaves,

making great efforts to justify this theory.

Thus, slavery in Europe and the Americas acquired a racial basis,

making it impossible for slaves and their future descendants

to attain equal status in society.

In all of these ways,

the Atlantic slave trade was an injustice on a massive scale

whose impact has continued long after its abolition.