Ulster will fight
During the political battles over Home Rule that stretched from the 1870s to the early 90s, the phrase "For Ulster will fight, and Ulster will be right" became a rallying cry for the Protestant Unionists in the North who wished to defeat the movement. Stephen scathingly (though silently) recalls this recent verbal bauble of the loyalists, just as he earlier thought of older cultural memes: "Glorious, pious and immortal memory. . . . The black north and true blue bible. Croppies lie down."
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.