Good question, Paddy. I asked my friend Bart who grew up in Inverin, Co. Galway and says he learned it from a man in the town. "Tír na Long" roughly translated is the "Land of Ships". He told me "It's far away from where he's living". Amráin Chlainne Gael identifies the place as Sasana, England, but gives no explanation how that phrase came about. I assume this song came out of a period of both intense poverty and recruitment by the British.