The phrase was coined in 1886 by Lord Randolph Henry
Spencer-Churchill (1849-95), a British aristocrat and
Conservative parliamentarian with no particular connection to
Ireland. Churchill fiercely opposed Gladstone's Home Rule
policy and attacked it in some passionate speeches in Ulster.
Thornton notes that Churchill's son and biographer, Winston,
wrote that "The jingling phrase, 'Ulster will fight, and
Ulster will be right,' was everywhere caught up. It became one
of the war-cries of the time and sped with spirit-speed all
over the country."
As Thornton also notes, the name "Ulster" is ambiguous.
Churchill used his phrase to appeal to the reactionary
Protestants in cities like Belfast and Londonderry, and the
northern part of Ireland that has remained in the UK since
independence in 1922 is now often called Ulster. But Ulster is
larger than Northern Ireland. It is one of the four ancient
provinces of Ireland, and until the plantations of the 17th
century it was the most Gaelic part of Ireland. Three of its
nine counties elected to join the Republic at independence.
County Donegal is particularly notable as a very Catholic and
Gaelic part of Ulster that would not have rallied to the
anti-nationalist sentiments of Churchill's jingoistic warcry.