A new book on Barack Obama's Irish roots has revealed that many of his Irish ancestors likely emigrated after the wig trade went downhill, when all high level professional jobs were moved to England after the Act of Union in 1800.

Author Steven McDonagh of Brandon Books explains in '”Barack Obama -- the Road From Moneygall” that the prosperity of the Dublin branch of the Kearney family, related to Obama's mother, was greatly damaged by the end of the wig trade.

Back then, people of all the professions wore wigs because it was believed that washing hair with water spread disease.

Obama's ancestors were among the best wig makers in Ireland, but the business collapsed when the seat of power was moved from the Irish parliament in Dublin to London and the professional classes were decimated.

The family had thus to look elsewhere and many turned to emigration.

The book traces the Irish link to Obama from the first emigrant, Thomas Kearney from Moneygall in Offaly  who was born in 1765, emigrated  in the 1780s and arrived in the port of Baltimore, Maryland, where he got married in 1791.

Every subsequent Kearney emigration, including that of Obama's direct ancestor Fulmouth Kearney, stems from Thomas Kearney's original trip into exile.

Some time later, Thomas went west, travelling the Wilderness Road into the frontier where land was available.

He settled in a remote settled in a valley in what would eventually become the state of Ohio.

Many of his relatives from Ireland followed him to the area and even today their graves are visible in small local cemeteries.

One of the best-preserved gravestones is that of another Thomas Kearney, a nephew of the original exile. Thomas was born in the King's County (Offaly) in 1800, and died in Ohio in 1845.

The incredible journey climaxed 160 years after Joseph Kearney arrived as an immigrant in 1849 when  his great-great-great-great grandson became president.