National and International Campaigns

The ending of the slave trade came about in two stages in most countries. The first was a struggle to pass formal laws against human trafficking, and the second was the fight to make those laws effective in the face of the newly illegal traffic, which in most cases continued for several decades after it was outlawed. Unlike the struggle against slavery itself, which was fought within the confines of each state, there was always a strong international component in the campaign against the slave trade. Many nations took action only after signing treaties, and the issue became inextricably intertwined with the emergence of international law, the definition of piracy, and the thorny question of intervention by one sovereign state in the affairs of another, in the face of what today would be called human rights abuses.

The narrative of formal abolition of the slave trade is straightforward given that it was completed in less than four decades — a rather striking fact considering that long-distance slave trading had been an acceptable commerce very likely since before the first written records. Paradoxically, what proved to be the first move against the slave trade was actually a device to preserve the institution.

In 1787, as part of the accommodation between northern and southern states, the U.S. Constitution prohibited any federal interference with the international slave trade for twenty years. But the U.S. Congress interpreted the provision as a permit to intervene as soon as the twenty years were up. By then, individual states had prohibited their citizens from participating in the slave trade from Africa.

But the first national initiative was taken by the Danes, who in 1792 passed legislation decreeing the end of the African trade, to take effect in 1802. The United States federal government banned the traffic outright on March 2, 1807, but left sufficient loopholes so that, each year until about 1820, a few hundred enslaved Africans continued to arrive in the U.S. legally, apart from those smuggled in. Later in the same month the British, who had come close to abolishing their own very large traffic several times after 1787, followed suit, and thus, in just five years, nations that had controlled almost half the transatlantic slave trade declared the traffic illegal.

This was a false dawn. Whenever a branch of the slave trade was interdicted, even if the ban was effective, there was always the question of how quickly other nations would simply fill the resulting gap, thus leaving the volume of the trade unaffected. Getting all nations to agree to formal abolition took another quarter century. In 1814, a major slaving nation, Holland, decreed abolition of her traffic (though the last authentically Dutch slaver had probably sailed five years earlier).

The Portuguese undertook to give up their traffic north of the equator in a treaty with Britain the following year, though the charter outlawing it dates only from the beginning of 1818. But the much larger Portuguese southern Atlantic trade remained legal for another eighteen years. A French abolition law passed in April 1818, though it added nothing to the administrative instructions of 1815 to treat Africans arriving in French colonies as "smuggled goods", while the Spanish crown, again in response to a treaty with the British, promulgated a cedula that took effect in 1820 and incorporated the terms of the treaty.

This left Brazil, an independent nation since 1822 (but an inheritor of all Portuguese treaty obligations until that point), with a trade south of the equator that was still within the law in Portuguese, if not British, eyes. The first Brazilian measure banning the traffic passed in November 1831 — before the Portuguese themselves took action. With every one of these national measures (except for the Dutch case), there was, however, a gap, measured in decades, between the proscription and the effective enforcement of the law. At least 1.5 million Africans arrived in the Americas in violation of the various laws against the slave trade.