Food historians generally agree colcannon belongs to the Irish. This conclusion is based on linguistic evidence, ingredient availability, and culinary preference. Combinations of potatoes, cabbage, and leeks were also embraced by many other cultures and cuisines, most notably Germany, Russia, France, Scotland, England. These hardy, economical, filling foods sated the bellies of the working and poorer classes.
Cabbages and their cousins were known to ancient cooks. They were thought to have several medicinal attributes. The Romans are said to have introduced cabbages to Europe, with the possible exception of Ireland, where [According to C. Anne Wilson/Food and Drink in Britain(1973)], linguistic evidence suggests it was already known to Iron Age Celts. In Medieval Europe cabbage/cole (often in combination with members of the onion family) were the food of the common man. Potatoes were introduced to to Europe by 16th century explorers. They were first regarded as curiosities, not readily embraced as food. The French, then the Irish, were among the first to recognize the fact that potatoes could keep a nation from starving. Recipes for potato and cabbage dishes were inevitable. These dishes developed according to collective taste and culinary experience.
"Colcannon. Originally and Irish dish of boiled potatoes and cabbage or kale mashed together and flavoured with onion, shallots, or leeks and cream or butter...The word 'colcannon' is from the Gaelic cal ceannann' which literally means white-headed cabbage. However, the cannon' part of the name might be a derivative of the old Irish cainnenn', translated variously as garlic, onion, or llek. Therefore it can be suggested that in its earliest form colcannon may have been a simple mixture of some brassica and allium. One of the earliest Irish references to the dish as a mash of potatoes and cabbages is found in the Diary of Wiliam Bulkely, of Bryndda, near Amlwch in Anglesey, who made two journeys to Dublin in 1735...The dish was introduced into England in the 18th century, where it became a favorite of the upper classes..In Ireland colcannon was associated traditionally with Halloween (31 October) festivities, when it was used for the purposes of marriage divination. Charms hidden in bowls of colcannon were portents of a marriage proposal should unmarried girls be lucky enough to find them, whilst others filled their socks with spoonfuls of colcannon and hung them from the handle of the front door in the belief that the first man through the door would become their future husband."