Tea is now so familiar a drink that it is easy to forget that, for most of its history, it was a commodity of great rarity outside the regions where it grew. Cultivated as a beverage in China for at least two thousand years, it remained largely unknown in Europe until the seventeenth century, when small quantities began to reach Portuguese and Dutch merchants through Indian Ocean trade. The subsequent global spread of tea - the creation of plantations in India, Ceylon and later Africa; the reshaping of trade routes; the political disputes that the trade provoked - is a reminder that a simple domestic habit can have consequences of considerable scope.

The tea plant, Camellia sinensis, is an evergreen shrub native to the border region between China, Myanmar and north-east India. When its young leaves are picked, dried and processed, they produce a drink whose caffeine and polyphenol content makes it mildly stimulating and notably refreshing. The processing varies by region: Chinese green tea is withered and heated rapidly to stop oxidation; Indian black tea is rolled and fully oxidised before drying; Japanese matcha is ground to a fine powder. Each approach produces a different flavour profile, and each has cultural associations that make easy substitution difficult.

Tea entered European trade through the Dutch East India Company in the early seventeenth century, initially as a luxury. It reached England via the court of Charles II, whose Portuguese queen, Catherine of Braganza, brought with her a taste for the drink and a supply of Chinese leaves. For the next century, all tea consumed in Europe came from China, and the Chinese authorities kept tight control over which ports were open to foreign merchants. This arrangement suited China but strained European trade: vast silver payments flowed eastwards, and there were few European goods that Chinese consumers wanted in return.

The East India Company, chartered in London in 1600, eventually resolved this imbalance in a manner that shaped nineteenth-century history. By the 1820s, the Company had begun shipping large quantities of opium, grown in India, to China, using the proceeds to pay for tea. The trade was illegal under Chinese law but enormously profitable, and it provoked the Opium Wars of the 1840s and 1850s. As part of the subsequent settlements, China ceded Hong Kong to Britain, opened further ports to foreign commerce, and paid heavy indemnities. Tea, though a minor presence in these events, was the economic motive for the imbalance that provoked them.

In parallel, the Company began to break China's monopoly by developing tea cultivation within British India. A native tea plant had been identified in Assam in the 1820s, and by the 1840s systematic plantations were being established there and in Darjeeling. The Scottish botanist Robert Fortune travelled in disguise through Chinese tea-growing regions between 1848 and 1851, studying manufacturing techniques and exporting both plants and skilled workers to the British operations. Within thirty years, Indian and Ceylonese tea had become the dominant supply for the British market, and Chinese exports to Britain had collapsed.

The social consequences of cheap, abundant tea were substantial. In Britain, tea replaced weaker beer as the everyday drink of working families, contributing to lower alcohol consumption over the nineteenth century. Sugar consumption rose in parallel, and the combined trade in tea and sugar reshaped the economies of colonies in the Caribbean and South Asia. Economic historian Dr. Priya Bhattacharya has argued that the popular image of tea as a symbol of British domesticity is historically misleading: the reality of the trade involved forced labour in Caribbean sugar plantations, indentured workers in Assam tea estates, and military coercion in Chinese ports.

In the twentieth century, tea production spread to Kenya, Indonesia, Argentina and several other countries, and the market became less concentrated. Kenya is now among the world's largest exporters. The industry remains labour-intensive at the picking stage, despite experiments with mechanical harvesters; the quality of the finest teas still depends on hand-picking of young leaves. Dr. Bhattacharya's recent work has looked at wages on East African tea estates and concluded that, in many cases, real incomes have not risen as quickly as the international retail price of tea might suggest. The story of tea, she writes, is a story of a drink that travelled far from its origins, but whose economic distances remain long.