The Portuguese spent the best part of a century working their way down the coast of Africa before they finally found its southern tip and the gateway into the Indian Ocean. The captain who first made the voyage from the cape across the Indian Ocean was Vasco da Gama, in 1497–98. He realised that, in order to cross the south Atlantic and round the tip of Africa, his best option would be to navigate a huge loop through the deep ocean in order to keep with the favourable winds and currents. This route took over three months and covered around 6,000 miles at sea – by far the longest voyage through open ocean undertaken by that time.

Even before da Gama’s pioneering voyage, Christopher Columbus had secured sponsorship from Spain for a westward voyage, and in 1492 sailed across the Atlantic to find a sea route to the riches of the Orient. Setting off from the Canary Islands, his fleet sailed with the easterly trade winds and unexpectedly ran into a whole new continental land mass – though, famously, he didn’t grasp that fact at the time. After mapping Caribbean islands for a few months, Columbus turned for home, first sailing north to pick up the band of westerly winds that blows through the Azores and which carried him back to Europe.

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Within a generation of that first voyage around the tip of South Africa, and of Columbus’s ‘discovery’ of the Americas, European sailors ventured across all the world’s oceans and completed the first circumnavigation of the Earth. This was a revolution that heralded the birth of today’s global economy.

This leap forward in long-distance exploration was possible because mariners came to understand the patterns of reliable winds and ocean currents around the globe, which now determined the trade routes that brought great riches to Europe. It was realised, for example, that the band of prevailing winds blowing to the west in the North Atlantic has a mirror-image counterpart in the southern hemisphere, and that the band of winds that enabled the return voyage back to Europe across the Atlantic Ocean are also present in the Pacific. There is a global pattern to the winds, caused by the fundamental circulation systems of the planet’s atmosphere.

Essentially, prevailing winds blow from the north-east in the zone between the equator and 30°N, and from the south-east between 30°S and the equator. Above 30°N and below 30°S, prevailing winds blow from the west. So If you want to sail to the Americas from Europe, simply head south a little bit first to position yourself in the zone of the trade winds and ride them all the way across the Atlantic. To get home again, you need a band of prevailing winds blowing in the opposite direction.

These alternating bands of prevailing winds – the trade winds and the westerlies – also blow the sea surface into great circling currents known as the ocean gyres. Because water is so much more dense than air, these ocean currents can have a significant impact on a ship’s course. An example is the Gulf Stream, which is part of the North Atlantic gyre flowing from the Caribbean to Scandinavia.

When was the Gulf Stream first discovered?

The Gulf Stream was discovered by European sailors in 1513, and the implications for shipping were immediately realised. Heavily laden galleons needed only slip into this wide, fast-flowing river-within-an-ocean to be readily carried north to where they could pick up the westerly winds to sail back to Europe.

Navigators also learned to be wary of regions around the world where the surface winds are light and variable, such as the zone along the equator within the rising arm of the Hadley cells – a potentially treacherous zone known to sailors as the doldrums.

As navigators decoded these global patterns of alternating bands of prevailing winds and wheeling ocean currents, they realised that they could use them as a great interlinked system of conveyor belts to carry them where they wanted to go. European sailors reached across the great expanses of the world’s oceans, established long-range maritime trade routes, and controlled and protected all of these overseas interests with their powerful gunpowder weapons.

By doing so, Portugal and Spain created a new kind of empire – one made powerful and wealthy not through possession of large areas of land territory but by the strategic control of sprawling oceanic trade networks on the other side of the world: empires of water. And where the Spanish and Portuguese led the way, the Dutch, British and French followed. The rivalry between these marine trading powers triggered colonial wars around the world as they attempted to eject each other from strategic ports and forts, to control chokepoints and dominate the critical sea passages. Europe was no longer a backwards extremity of Eurasia, but had extended itself to dictate affairs around the world – for better or for worse.

After the course from Europe to India around the southern tip of Africa had been pioneered by Vasco da Gama, the Portuguese began sending annual expeditions along this long maritime route. Indeed, the very first fleet that followed da Gama’s route to India took such a wide loop through the south Atlantic that they stumbled on the Brazilian coastline.

By 1520, the Portuguese had asserted their dominance across the Indian Ocean and the so-called Spice Islands (now Maluku, an archipelago within Indonesia) with their large, cannon-wielding ships and fortress-building techniques – experience gained from centuries of incessant warfare in Europe – and grew hugely wealthy by monopolising this trade. Portugal also established trading centres in Macau and Nagasaki to conduct business directly with the Chinese and Japanese. The Strait of Malacca, between the Malay peninsula and the long island of Sumatra (also now part of Indonesia), became a crucial maritime chokepoint, serving as the gateway into the archipelagos of south-east Asia; the Portuguese colony of Malacca (now Melaka) thus became the primary port controlling maritime traffic through the Strait.

The impact of their discovery was longer-lasting than the wealth it generated. Even after the trade dominance of the Portuguese empire waned and Brazil declared independence in 1822, their colonies endured for well over a century longer. The enclaves of Goa, Daman and Diu became part of India in 1961; Portuguese Timor was relinquished in 1975, the same year that Angola and Mozambique became independent; and Macau was finally handed over to China in 1999. Even today, Portuguese remains the primary official language of Brazil, Angola, Mozambique and other former colonies including Cape Verde, and the language (or a form of Portuguese Creole) is spoken in East Timor, Goa, Daman and Diu.

Familiar patterns

In the early 16th century, Spanish navigators found a route around the tip of South America and across the Pacific with the trade winds to the Spice Islands – but they also had to find a way to get their newly traded goods home. They realised that the now-familiar circular pattern of winds in the Atlantic was replicated in the Pacific, and navigators learned to sail first north from the Philippines to Japan before picking up the westerlies to carry them all the way east to the Californian coast.

For 250 years, this Manila Galleon Route bridged the vast Pacific Ocean with regular round-trip shipping, running between the Spanish colonies in Acapulco (in present-day Mexico) and Manila in the Philippines. Silver mined from the Americas was traded with the Chinese for luxuries such as silk, porcelain and spices. California thus became hugely important to the Spanish simply because it was where the winds delivered them after their transpacific crossing from Asia, and cities such San Francisco, Los Angeles and San Diego were founded to resupply Spanish ships after they had completed this long voyage.

In 1610–11, the Dutch found a shortcut bypassing part of the original Portuguese route to the Spice Islands. Rather than tracing the coast all the way around the northern Indian Ocean, which forced ships to wait for the correct monsoon winds to reach their goal, Captain Hendrik Brouwer of the Dutch East India Company recognised that it was quicker to sail straight east from the tip of South Africa before heading north at the eastern edge of the Indian Ocean.

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The westerly winds that flow around the southern hemisphere are largely unobstructed by continents or mountains, so they blow far more strongly than their northern counterparts. These ‘Roaring Forties’ create what’s effectively a fast-moving motorway in the ocean, with the result that the time taken to sail the Brouwer Route was half that of the traditional passage – around six months, rather than a full year. It also had another notable impact: the critical gateway into the East Indies, which had been the Strait of Malacca, became the Sunda Strait between Java and Sumatra, and the Dutch colony of Batavia (present-day Jakarta) replaced Portuguese Malacca as the key strategic port in the region.

In 1652, the Dutch founded a colony at Cape Town to resupply ships that were about to undertake the long voyage across the chill southern waters of the Indian Ocean – hence this use of the Roaring Forties wind belt is the reason why Afrikaans (which is derived from the Dutch spoken by 17th-century settlers) is spoken today in South Africa. The Dutch East Indies, headquartered in Batavia, became the dominant trade power in that part of south-east Asia as a result, expanding its control to encompass all of what’s now Indonesia until the Second World War.

Whereas the quest for spices had been the prime motivation during the early years of the Age of Exploration, by 1700 other commodities were beginning to dominate oceanic trade. Crops such as cotton, sugar, tobacco and coffee had been transported to and grown in plantations in the Americas, creating a high demand for labour to produce them in mass for European markets.

The Atlantic triangular trade that emerged from the late 16th century had arguably the greatest impact on the modern world. Though Portuguese traders began transporting slaves from the west African coast to Brazil around 1502, it was during the following century that the triangular trade became the primary pattern for English, French, Portuguese and Dutch.

The huge economic cog of the triangular trade, conveniently powered by the wind patterns of the Atlantic, generated huge profits for its masters

Ships involved in this trade sailed south from Europe laden with goods such as textiles and weapons manufactured in these developed nations; these were sold on the west African coast. Those cargoes were replaced by enslaved people who had been captured in west and central Africa, and who were sold to the European traders. Transported west across the Atlantic, these people were sold to plantation owners in Brazil, the Caribbean and North America; the ships then carried the produce of slaves’ forced labour in the New World – sugar, cotton and tobacco, in particular – back to Europe (and, sometimes, New England, where sugar was used to distil rum) to complete the loop.

Each turn of this huge economic cog, conveniently powered by the wind patterns of the Atlantic, generated huge profits for its masters, and the supply of cheap overseas cotton helped drive mechanisation in the early stages of the Industrial Revolution in Britain in the latter 18th century.

It’s clear, then, that the pattern of winds and fundamental circulation systems within Earth’s atmosphere determined the routes of huge continent-linking trade networks – and, therefore, the pattern of colonisation and empire-building that emerged during the modern era, planting the foundations of globalisation and the modern world.

Lewis Dartnell is a professor at the University of Westminster, and the author of Origins: How the Earth Made Us (Bodley Head, 2019)

This article was taken from issue 17 of BBC World Histories magazine

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