They called them the Improvers - but they brought so much tragedy and misery to the Highlands that they are still hated to this day.

The Highland Clearances are still regarded as one of the most shameful episodes in Scottish history. Whole families were forced off the land and literally chased to the ends of the Earth - to make way for sheep.

Tens of thousands of people were evicted from the lands which their families had held for generations by the ruthless factors of landlords who were often absentees. In many cases terrified Highlanders were burned out of their homes and entire glens emptied.

In many cases, these wretched tenants only found peace and managed to build a new life for themselves by sailing across the Atlantic to America and Canada.

Highlanders had always face a struggle living off the land - but, until the Jacobite defeat at Culloden in 1746, they had been protected to some extent by the Clan system, which assured they paid fair rents and their basic needs were met.

After Culloden, the population of the Highlands actually increased, largely because of the beginning of potato planting and advances in medical treatment. However, this created its own problems - with more people living off the same relatively unproductive land, there were fewer resources to go round.

As a result, emigration started, and it increased in the 1780s after the American War of Independence. Even before then, however, people were sailing off to try and make a life for themselves in North America.

The end of the clan system after Culloden made the work of the tacksmen - the men who collected rents on behalf of the chief - redundant. Many of them left Scotland, taking their families and often their local communities with them.

The real pressure for change in the Highlands, however, came when the so-called Improvers - those who sought to make the difficult Highland economy more productive - realised that they could make good money out of populating the area with sheep.

The economic advantages were obvious. Many Highlanders scrabbled a living off poor quality cattle, but by the 1770s, the demand for wool had grown and its price had doubled in just ten years. In addition, the animals could also be slaughtered for mutton.

Contrary to popular belief, Highlanders were not simply torn from their lands and put on boats to North America. The process was a much more subtle one than that.

Initially, they were moved to the coast to places such as Thurso and Brora where it was believed they could make a living in other industries such as fishing or kelping - the processing of seaweed into alkali, which was also a booming trade at the time and was highly labour intensive.

The Highlanders had no choice about leaving the land of their ancestors. They simply didn't have the cash or the experience to buy sheep and tend them. Instead, sheep farmers who did have the necessary background were brought in by the landlords from the lowlands or England.

The landlords believed that by moving their subjects to the coast, they would be able to earn a far better living than they could off the impoverished Highland land.

Those who were moved were given small parcels of land known as crofts, and they became known as crofters for the first time. However, it often wasn't of much use to them. Sometimes it was so poor that they were forced into industries such as kelping anyway.

Even if the land was productive, the luckless tenants were often charged such extortionate rents that they couldn't afford the land - once again forcing them to look to other forms of work.

If tenants tried to stay on their existing lands in the Highland glens, the local factors usually removed them by using brutal force. A favoured method was to pull down the roofs of their homes while they looked on and then set fire to the roof tresses to ensure that they could not be rebuilt.

Some of the evictors, such as Patrick Sellar, the factor who worked for the Countess of Sutherland, acted despicably. Sellar personally directed the clearance of 430 people from Strathnavar, and was charged with the murder of an old woman of whom he is said to have remarked: "She has lived too long - let her burn."

The trial was held in Inverness, but the jury was packed with local landowners and Sellar was found not guilty and allowed to carry on with his work. The law officer who brought the charge against him was sacked.

The Countess of Sutherland and her husband the Marquis of Stafford were regarded as the worst landlords of all. By 1811, some 15,000 of their tenants had been moved to make way for sheep, with huge social and economic consequences. The brutal work of thugs such as Sellar only served to increase their notoriety further.

As people flocked to the coast in one of the worst instances of ethnic cleansing ever seen in Scotland, problems increased. Too many people were trying to milk the natural resources to keep themselves alive. This resulted, for instance, in over-kelping.

Giving the highlanders the opportunity to make a living from fishing also proved to be little short of a disaster, since they had little or no knowledge of how to do this. When they were able to exploit the industry successfully, it simply led to overfishing.

Until the 1820s, there had only been a trickle of emigrants, but then the economy took a turn for the worse and the vibrant kelp industry collapsed. Another problem was that the price of cattle - still an important agricultural commodity - fell. To heap on the misery further, the 1830s and 1840s saw the failure of the potato crop, which until then had provided Highlanders with a staple food.

With people being made destitute and the Highlands completely unable to support them, some people headed south to try and find work in the new urban centres such as Glasgow. But many turned to the colonies as their only means of escape from hardship.

By this stage, the landlords were prepared to pay for their travel, since transportation avoided having to find some form of work for them and disposed of the problem of keeping them. For many of the emigrants, there was really no other choice - if they wanted to continue to work the land, they literally had nowhere else to go.

Once in Canada, Scots helped to open up the country, settling in places such as Prince Edward Island, Manitoba and the remote north west and working parcels of land which were assigned to them.

There is also little doubt that Scots shaped the history of the continent. By populating the Red River area of Manitoba, for instance, they established a British settlement there and stopped the Americans from advancing up as far as Hudson's Bay.

If the Scottish settlement had not existed and the by-then independent Americans had been able to push north, then Canada would certainly not exist in its present form today.

But the Clearances changed the Highlands forever, too. Where once cattle had roamed and whole clans had lived, there were now nothing but sheep enclosures and the odd solitary shepherd.

The hatred over what the factors and the sheep farmers did to the ordinary folk of the Highlands lingers to this day - and also helps to explain why, dotted around this remote landscape, you can still see the evidence of long abandoned settlements.