Gaelic speech to a significant extent. Historically, the "Highland line" distinguished the two Scottish cultures. While the Highland line broadly followed the geography of the Grampians in the south, it continued in the north, cutting off the north-eastern areas, that is Eastern Caithness, Orkney and Shetland, from the more Gaelic Highlands and Hebrides. Historically, the major social unit of the Highlands was the clan. Scottish kings, particularly James VI, saw clans as a challenge to their authority; the Highlands was seen by many as a lawless region. The Scots of the Lowlands viewed the Highlanders as backwards and more "Irish". The Highlands were seen as the overspill of Gaelic Ireland. They made this distinction by separating Germanic "Scots" English and the Gaelic by renaming it "Erse" a play on Eire. Following the Union of the Crowns, James VI had the military strength to back up any attempts to impose some control. The result was, in 1609, the Statutes of Iona which started the process of integrating clan leaders into Scottish society. The gradual changes continued into the 19th century, as clan chiefs thought of themselves less as patriarchal leaders of their people and more as commercial landlords. The first effect on the clansmen who were their tenants was the change to rents being payable in money rather than in kind. Later, rents were increased as Highland landowners sought to increase their income. This was followed, mostly in the period 1760–1850, by agricultural improvement that often (particularly in the Western Highlands) involved clearance of the population to make way for large scale sheep farms. Displaced tenants were set up in crofting communities in the process. The crofts were intended not to provide all the needs of their occupiers; they were expected to work in other industries such as kelping and fishing. Crofters came to rely substantially on seasonal migrant work, particularly in the Lowlands. This gave impetus to the learning of English, which was seen by many rural Gaelic speakers to be the essential "language of work". Older historiography attributes the collapse of the clan system to the aftermath of the Jacobite risings. This is now thought less influential by historians. Following the Jacobite rising of 1745 the British government enacted a series of laws to try to suppress the clan system, including bans on the bearing of arms and the wearing of tartan, and limitations on the activities of the