O'Donnell Abú (O'Donnell Forever), also known as the Tyrconnel War Song, was written in the mid-19^th 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.