Conversely, the second half of the 18th century saw the Highland population increase dramatically after the introduction of the easy-to-grow and nutritious potato. Between 1745 and 1811, the population of the Outer Hebrides, for example, rose from 13,000 to 24,500. The clan chiefs adopted different policies to deal with the new situation. Some encouraged emigration, and as many as 6000 Highlanders left for the Americas between 1800 and 1803 alone. Other landowners developed alternative forms of employment for their tenantry, mainly fishing and kelping. Kelp (brown seaweed) was gathered and burnt to produce soda ash, which was used in the manufacture of soap, glass and explosives. There was a rising market for soda ash until the 1810s, with the price increasing from £2 a ton in 1760 to £20 in 1808, making a fortune for some landowners and providing thousands of Highlanders with temporary employment. Other landowners developed sheep runs on the Highland pastures, introducing hardy breeds like the black-faced Linton and the Cheviot. But extensive sheep farming proved incompatible with a high peasant population, and many landowners decided to clear their estates of tenants, some of whom were forcibly moved to tiny plots of marginal land, where they were to farm as crofters.

'Evictions were carried out with considerable brutality. Those who failed to leave by the appointed time had their homes burnt in front of them'

The pace of these Highland Clearances accelerated after the end of the Napoleonic Wars in 1815, when the market price for kelp, fish and cattle declined, leaving sheep as the only profitable Highland product. The most notorious Clearances took place on the estates of the Countess of Sutherland, who owned a million acres in northern Scotland. Between 1807 and 1821, around 15,000 people were thrown off her land, evictions carried out by Patrick Sellar, the estate factor, with considerable brutality. Those who failed to leave by the appointed time had their homes burnt in front of them, and one elderly woman, who failed to get out of her home after it was torched, subsequently died from her burns. The local sheriff charged Sellar with her death, but a jury of landowners acquitted him, and the sheriff was sacked. As the dispossessed Highlanders scratched a living from the acid soils of tiny crofts, they learnt through bitter experience the limitations of the clan. Famine followed, forcing large-scale emigration to America and Canada and leaving the huge uninhabited areas found in the region today.

The crofters eked out a precarious existence, but they hung on throughout the 19th century, often by taking seasonal employment away from home. In the 1880s, however, a sharp downturn in agricultural prices made it difficult for many crofters to pay their rent. This time, inspired by the example of the Irish Land League, they resisted eviction, forming the Highland Land Reform Association and the Crofters' Party. In 1886, in response to the social unrest, Gladstone's Liberal government passed the Crofters' Holdings Act, which conceded three of the crofters' demands: security of tenure, fair rents to be decided independently, and the right to pass on crofts by inheritance. But Gladstone did not attempt to increase the amount of land available for crofting, and shortage of land remained a major problem until the Land Settlement Act of 1919 made provision for the creation of new crofts. Nevertheless, the population of the Highlands has continued to decline since then, with many of the region's young people finding city life more appealing.