The woman of the song returning as a liberator, Gráinne Mhaol (sometimes known as Grace O'Malley) was chieftain of the Ó Máille clan in the west of Ireland. She is a well-known historical figure in 16th-century Irish history, and is sometimes known as 'The Sea Queen of Connacht', one of the most famous female pirates of all time.

In a nutshell, in 1578 Gráinne Mhaol (whose name was already pretty famous at the time) was thrown into the dungeons of Dublin Castle by the local English Governor, but was later released from prison by the English on the pretext of bringing Risdeárd an Iarainn Bourke (Richard-in-Iron, Gráinne's 2nd husband) and his fellow Irish rioters to heel.
As soon as she was released, reunited with her husband, Gráinne started plundering English shipping and managed to rout an English army sent to beseige her.
The following year Gráinne and Bourke went into rebellion once again to secure their rights (she was accused to be 'nurse to all rebellions in that province for over forty years')

Almost 15 years later Elizabeth I imprisoned Gráinne Mhaol's sons and half-brother, forcing Gráinne to negotiate their release. Even though she refused to bow before Elizabeth (as she did not recognise her as the Queen of Ireland), the talks led to the release of her family, under the agreement that Gráinne would stop attacking English ships.
Realising the meeting was useless, Gráinne went back to attacking English ships shortly after her departure.

Complete timeline: http://www.graceomalley.com/index.php/grace-omalley/time-line

Óró, 'sé do bheatha 'bhaile is a traditional Irish song associated with the Jacobite cause (dating to the third Jacobite rising of 1745-6). In the early 20th century it received new verses by the nationalist poet Pádraig Pearse and was often sung by members of the Irish Volunteers during the Easter Rising (April 1916). It was also sung during the Irish War of Independence (1919-1921).


Notes:

óglaigh → óglaigh means armed youths/young warriors - it later became 'volunteers' in the current sense (Óglaigh na hÉireann = the Irish Volunteers)

Gallaibh → Gallaibh means ‘among the strangers’. Gall ‘stranger/foreigner’ in this case denotes non-Irish speakers. The ending -aibh represents an old dative plural meaning ‘among’ (i.e. 'the town/land of the foreigners'). The term was originally used to denote any area where non-Irish speakers were settled.
The word Gallaibh as a synecdoche (that is to say meaning 'foreigners') includes both the Seanghaill (lit. 'old foreigners', the older Anglo-Norman or English settlers in Ireland) and the Nuaghaill ('new foreigners', the later Anglo-Norman or English settlers in Ireland)



Kindly suggested by Kiara Thompson :)


Performed by Paul Brady and Iarla Ó Lionáird
Album: Anam An Amhráin (by Sónta & Cartoon Saloon for TG4)
Original animation: https://vimeo.com/25229012