O'Donnell Abú (O'Donnell Forever), also known as the Tyrconnel War Song, was written in the mid-19th century by one Michael McCann. It's a rousing marching song about the Nine Years War (1594 – 1603), when O'Neill and O'Donnell challenged Elizabethan rule in Ireland.
Proudly the note of the trumpet is sounding Loudly the war-cries arise on the gale Fleetly the steed by Lough Swilly is bounding To join the thick squadrons on Saimer's green vale On, every mountaineer, strangers to flight of fear Rush to the standard of dauntless Red Hugh Buanadha and gallowglass throng from each mountain pass Onward for Erin, O'Donnell Abú Princely O'Neill to our aid is advancing With many a chieftain and warrior clan A thousand proud steeds in his vanguard are prancing 'Neath the borderers brave from the banks of the Bann Many a heart shall quail under its coat-of-mail Deeply the merciless foeman shall rue When on his ear shall ring, borne on the breeze's wing Tír Conaill's dread war-cry: "O'Donnell Abú" Wily old Desmond the war-wolf is howling Fearless the eagle sweeps over the plain The fox in the streets of the city is prowling And all who would scare them are banished or slain On with O'Donnell then, fight the old fight again Sons of Tír Conaill are valiant and true Make the proud Saxon feel Erin's avenging steel Strike for your country, O'Donnell Abú
After losing the war, O'Neill and O'Donnell left Ireland, never to return (the Flight of Earls). Their lands were colonized by English and Scottish Protestants (the Plantation of Ulster), hence the demographic complications of modern Northern Ireland.