Between 1501 and 1866, it is estimated that over 12.5 million people were forced onto ships in Africa, and transported to the Americas as slaves. Furthermore, it is estimated that only 10.7 million of these slaves disembarked on the other side of the Atlantic, meaning that roughly 1.8 million did not survive the journey. The transatlantic slave trade was a part of the triangular trade route between Europe, Africa and the Americas, during the sixteenth and nineteenth centuries. Generally speaking, this route saw European merchants bring manufactured products to Africa to trade for slaves, then transport the slaves to the Americas to harvest raw materials, before taking these materials back to Europe where they would then be consumed or used in manufacturing. Slavery was an integral part in funding the expansion of Europe's colonial empires, which shaped the modern and highly globalized world in which we live today.

The Middle Passage As with trade, the slave journey was also broken into three parts; the First Passage was the stage where slaves were captured and transported to African ports, the Middle Passage was the journey across the Atlantic, while the Final Passage was where the slaves were transported to their place of work. The death toll in the First Passage is thought to be the highest of the three stages, as millions were killed or fatally wounded as they were captured, however a lack of written data and historical evidence has made this number difficult to estimate. In contrast, shipping records from the time give a much more accurate picture of the Middle Passage's death toll, and this data suggest that roughly 14.5 percent of slaves did not survive the journey. The reason for this was the harsh and cramped conditions on board; slave ships were designed in such a way that they could fit the maximum number of slaves on board in order to maximize profits. These conditions then facilitated the spread of diseases, such as smallpox and dysentery, while malnutrition and thirst created further problems. Generally, slavers aimed to keep slaves as healthy (therefore; profitable) as possible, although there are countless examples of mistreatment and punishment of slaves by their captors, and several cases where slaves were exterminated by the crew as provisions ran low.

Rise and fall of the transatlantic slave trade

The European arrival in the Americas also saw the introduction of virgin soil epidemics (new diseases being introduced to biologically defenseless populations) which decimated the indigenous populations. The abundance of natural resources, but lack of available labor led to the rise of the transatlantic slave trade. Until the mid-1600s, Portuguese traders had a near-monopoly on this trade, supplying slaves to the newly expanding Spanish and Portuguese empires in South America. As other European powers began to expand their empires in the Caribbean and North America, the slave trade grew dramatically, and during the eighteenth century, the number of slaves being brought to the New World increased from an annual average of thirty thousand in the 1690s to 87 thousand in the 1790s. The transatlantic slave trade reached its peak between the 1750 and 1850, and an average of 74 thousand slaves were brought to the Americas each year between these dates. The largest decline came as the slave trade was disrupted during the American War of Independence (1775-1783), although the trade became weakened as the abolitionist movement gained momentum in Europe and the Americas around the turn of the century. The most significant impacts came as the slave trade was abolished in Britain and the U.S. in 1807 and Brazil in 1831, and Britain then used its position as the global superpower to impose abolition on other nations and used the Royal Navy to enforce these measures. While most nations abolished the slave trade in the early 1800s, it would take decades before the actual practice of slavery would be abolished; today, slavery is illegal in almost every country, however modern slavery in the forms of forced labor, human trafficking and sexual exploitation continues to be prevalent across the globe.

There were almost 700 thousand slaves in the US in 1790, which equated to approximately 18 percent of the total population, or roughly one in every six people. By 1860, the final census taken before the American Civil War, there were four million slaves in the South, compared with less than 0.5 million free African Americans in all of the US. Of the 4.4 million African Americans in the US before the war, almost four million of these people were held as slaves; meaning that for all African Americans living in the US in 1860, there was an 89 percent* chance that they lived in slavery. A brief history Trans-Atlantic slavery began in the early sixteenth century, when the Portuguese and Spanish forcefully brought captured African slaves to the New World, in order to work for them. The British Empire introduced slavery to North America on a large scale, and the economy of the British colonies there depended on slave labor, particularly regarding cotton, sugar and tobacco output. In the seventeenth and eighteenth century the number of slaves being brought to the Americas increased exponentially, and at the time of American independence it was legal in all thirteen colonies. Although slavery became increasingly prohibited in the north, the number of slaves remained high during this time as they were simply relocated or sold from the north to the south. It is also important to remember that the children of slaves were also viewed as property, and (apart from some very rare cases) were born into a life of slavery. Abolition and the American Civil War In the years that followed independence, the Northern States began gradually prohibiting slavery, and it was officially abolished there by 1805, and the importation of slave labor was prohibited nationwide from 1808 (although both still existed in practice after this). Business owners in the Southern States however depended on slave labor in order to meet the demand of their rapidly expanding industries, and the issue of slavery continued to polarize American society in the decades to come. This culminated in the election of President Abraham Lincoln in 1860, who promised to prohibit slavery in the newly acquired territories to the west, leading to the American Civil War from 1861 to 1865. Although the Confederacy (south) were victorious in much of the early stages of the war, the strength in numbers of the northern states (including many free, black men), eventually resulted in a victory for the Union (north), and the nationwide abolishment of slavery with the Thirteenth Amendment in 1865. Legacy In total, an estimated twelve to thirteen million Africans were transported to the Americas as slaves, and this does not include the high number who did not survive the journey (which was as high as 23 percent in some years). In the 150 years since the abolishment of slavery in the US, the African-American community have continuously campaigned for equal rights and opportunities that were not afforded to them along with freedom. The most prominent themes have been the Civil Rights Movement, voter suppression, mass incarceration and the relationship between the police and the African-American community has taken the spotlight in recent years.

This statistic shows the number of black men and women in the US from 1820 until 1880. Slavery was legal in the Southern States of the US until 1865, when the Thirteenth Amendment was added to the US Constitution after the American Civil War. Until that time all of the slaves included in this statistic were registered as living in the South, whereas the majority of the free, black men and women lived in the Northern States. From the data we can see that, while the slave experience was very different for men and women, there was relatively little difference between their numbers in each respective category. While female slaves were more likely to serve in domestic roles, they were also more likely to be working in the lowest and unskilled jobs on plantations, whereas men were given more skilled and physically demanding roles. As slavery was abolished in 1870, all black people from this point were considered free in the census data. It is also worth noticing that in these years the difference in the number of men and women increased, most likely as a result of all the black male soldiers who fell fighting in the American Civil War.

Knowledge regarding the prices paid for slaves during the transatlantic slave trade is quite scarce, however the data that does exist provides some insight into the financial value given to slaves during this period. The study shown here indicates that at certain intervals between 1638 and 1775, the average price paid for slaves in the Thirteen Colonies ranged from 16.5 to 44.08 pounds sterling for slaves from Britain's colonies in the Americas, and between 1.87 and 17.43 pounds for slaves transported from West Africa. It is important to note that the average prices given are from sample sizes of ranging between just one and 29 sales, therefore the numbers may be more reliable in some years than in others.

Despite these limitations, the data does show a clear difference between the prices for slaves who were born in the Americas or accustomed to its climate (known as "seasoned"), compared to those who had travelled from West Africa, as those were often weakened from the journey and susceptible to tropical disease, and therefore deemed less valuable. For example, in the period between 1713-17 (the group with the largest sample size), the average value of unseasoned slaves from West Africa was just 38.5% the value of seasoned slaves.

From 1501 until 1866, it is estimated that the transatlantic slave trade saw more than 12.5 million African people forcefully put on slave ships and transported to the Americas. Of these 12.5 million, only 10.7 million disembarked on the other side of the Atlantic, meaning that approximately 1.8 million (14.5 percent) did not survive the journey, known as the Middle Passage. Throughout most of the the sixteenth century, the mortality rate was around thirty percent, it then fell below twenty percent in the late seventeenth century, and below fifteen percent in the late eighteenth century. There was a slight increase in the mid-1800s, before the transatlantic slave trade effectively ended in the 1860s. The overall average mortality rate is lower than the rate in most decades, due to the larger numbers of captives transported in the late 1700s; a significant number of these voyages were between Africa and Brazil, which was generally the shortest of the major routes.

Of the first eighteen presidents of the United States, twelve owned slaves throughout their lifetime, and eight of these were slave owners while occupying the office of president. Of the U.S.' first twelve presidents, the only two never to own slaves were John Adams, and his son John Quincy Adams; the first of which famously said that the American Revolution would not be complete until all slaves were freed. George Washington, leader of the revolution and the first President of the United States, owned many slaves throughout his lifetime, with 123* at the time of his death. Historians believe that Washington's treatment of his slaves was typical of slaveowners in Virginia at the time, however he did develop moral issues with the institution of slavery following the revolution. Washington never publicly expressed his growing opposition to slavery, although he did stipulate in his will that all his slaves were to be freed following the death of his wife, and he made financial provisions for their care that lasted until the 1830s.

Jefferson controversies

In recent years, the legacy of Thomas Jefferson has come under the most scrutiny in relation to this matter; the man who penned the words "all men are created equal" is estimated to have owned at least 600 slaves throughout the course of his lifetime. Before becoming president, Jefferson argued for restrictions on the slave trade, and against its expansion into new US territories; however he avoided the subject during his presidency as the topic grew in divisiveness and he believed that emancipation would not be achieved during his lifetime. It is also widely accepted that Jefferson had an affair and likely fathered children with one of his slaves, Sally Hemmings, who is also believed to be the half-sister of Jefferson's first wife. DNA tests conducted in the 1990s confirmed a genetic link between the descendants of the Jefferson and Hemings families, but could not confirm whether the link was Jefferson himself or a relative; most historians however, believe that Jefferson fathered at least one of Sally Hemings' children, and possibly six or eight of them (all of whom were kept as Jefferson's slaves).

Other Presidents

Of the other presidents who appear on this list, all are regarded differently for their attitudes towards slavery, and their impact on the eventual abolition of slavery and the emancipation of slaves. Madison and Monroe grew up in slave-owning families, and owned a number of slaves while serving in the White House; interestingly, Monrovia, the capital city of Liberia (the country was founded by the American Colonization Society as an African settlement for freed slaves), was named in Monroe's honor as he was a prominent advocate of the ACS. Andrew Jackson, who earned a large portion of his private wealth via the slave trade, introduced legislation that protected slave owners and slavery in the southern states; he owned around 200 slaves at the time of his death, and many more throughout his lifetime. John Tyler publicly decried slavery and claimed that it was evil, although he owned slaves as he said this and his political actions in his later life actually supported the institution of slavery (Tyler is notably the only U.S. president whose death was not mourned officially as he was involved in the government of the Confederacy at the time).

Perhaps the most surprising names on this list are Andrew Johnson and Ulysses S Grant, the vice president and leader of the United States Army during the latter stages of the American Civil War. Neither men owned slaves while in office, although Johnson, the man who oversaw the ratification of the Thirteenth Amendment, is reported to have owned eight slaves before entering the world of politics. Ulysses S. Grant, who managed his wife's family's farm in the 1850s, inherited one slave in 1854 who he then freed two years later. Grant's armies would eventually free countless slaves in the 1860s, as he led the Union to victory against the Confederacy and brought an end to slavery in the United States.

This statistic shows the population of the United States in the final census year before the American Civil War, shown by race and gender. From the data we can see that there were almost 27 million white people, 4.5 million black people, and eighty thousand classed as 'other'. The proportions of men to women were different for each category, with roughly 700 thousand more white men than women, over 100 thousand more black women than men, and almost three times as many men than women in the 'other' category. The reason for the higher male numbers in the white and other categories is because men migrated to the US at a higher rate than women, while there is no concrete explanation for the statistic regarding black people.

Annual cotton production in the United States grew from just a few thousand tons at the turn of the 19th century, to fluctuating between 1.6 million and 4.3 million tons throughout most of the 20th century. The amount of space used to produce cotton also grew from three to almost 18 million hectares of land between 1866 and the 1920s, before dropping to around four or five million hectares between the 1960s and 1980s. Despite this drop in land usage, advancements in agricultural technology meant that output remained relatively constant in the 20th century, meaning that output per hectare actually increased significantly.

The mechanical cotton gin's invention in 1793 revolutionized the U.S. cotton industry, which grew exponentially in the early 19th century. Cotton was the U.S.' primary export in these years, and its production was driven by slave labor in the southern states (particularly South Carolina). For the first time, output exceeded one million tons in 1859, and again in 1861, however, the disruption of the American Civil War caused cotton output to drop by over 93 percent in the next three years, to just 68 thousand tons by 1864. Production resumed upon its previous trajectory following the war's end, and many of the former-slaves forced to work on cotton plantations continued to work in the cotton industry, but as sharecroppers who worked the land in exchange for a share of the harvest, as well as housing and facilities (this was similar to tenant farming, although sharecroppers received a smaller share of the crop and had fewer legal protections).

Throughout the 17th century, St Domingue (Haiti) was the largest producer of sugar in the world (unfortunately no annual data is available in this source); with the Haitian revolution in 1791, however, Haiti became the first independent state in the Caribbean, and its share of the international sugar market all-but disappeared. By the mid-1800s, European investment in Cuba led to it becoming the world leader in the sugar industry; a position it would hold until the 1960s, when it was overtaken by Brazil.

Slavery and the "sugar bowl of the world" The brief annexation of Cuba by the British in the 1760s saw an influx of investment from European merchants into Cuba's undermanned sugar plantations, who aimed to exploit Cuba's abundant resources and rival the dominance of St Domingue. With this investment and opening of international trade, plantation owners in Cuba began importing slave labor to meet the overwhelming demand; as a result, Cuba became one of the most common destinations for African slaves in the 19th century. Slavery was eventually abolished in Cuba in 1886, however this did little to disrupt Cuba's sugar output, and migrant workers were imported form Asia (namely, China) to meet labor demands.

From the data, the first major disruption to Cuba's sugar output came in the 1890s, during the Cuban War of Independence (1895-1898), when it dropped by over 77.5 percent between 1894 and 1895. Production increased significantly in the early 20th century, due to agricultural mechanization, and output was between four and five million metric tons in the late 1920s; however, the Great Depression then saw Cuba's sugar output drop from 5.2 million tons in 1928 to just 1.9 million tons by 1932. Annual output then grew significantly following the Second World War, exceeding five (sometimes even eight) million tons per year; nonetheless, output fluctuated greatly, with observable changes during milestone years in Cuban history, such as the military coup in the early 1950s, the Cuban Missile Crisis and U.S. trade embargo in 1962, and Castro's (failed) attempt to harvest ten million tons of sugar in 1970 to boost the Cuban economy.