Tens of thousands of Highlanders emigrated to other parts of Scotland and to England, North America, Australia and New Zealand between the 1760s and the 1880s after Scottish landlords evicted them from their small holdings so they could farm on a larger and more economic scale.
Prof Eric Richards, of Flinders University, Adelaide, an authority on British and Scottish migration, said the letters from those who left were "the pure gold of archival material" for historians as they were truly the voice of the people.
Uncovering more letters, some of which might be in New Zealand archives or still held by descendants, would help settle the "history wars" between those who denounced the clearances and those who defended them.
Prof Richards, in Dunedin to give three lectures, told an audience of more than 200 at the Otago Settlers Museum yesterday the denouncers used terms like genocide and ethnic cleansing and even drew parallels with the Jewish Holocaust.
However, the crofter farmers had no legal rights to occupy their land once they had been asked to leave, and others viewed the clearances as an unfortunate result of agricultural development.
"The clearances have polarised opinions . . . and in the great flood of controversy, academics have been left behind like shags on a rock."
Prof Richards said the emerging view was the clearances had to be considered in a wider context and over a longer time line.
Before and after the clearances, Highlanders caught in the poverty trap of too many children, falling commodity prices, uncertain employment prospects and a difficult climate and terrain for farming were leaving the land, he said.
"The clearances are a severe and dramatic version of the universal story of rural people leaving the land."
