The Flight of the Wild Geese

Not to be confused with the 1607 Flight of the Earls.

Uniform and colonel’s flag of the Hibernia Regiment, mid-eighteenth century
The Flight of the Wild Geese refers to the departure of an Irish Jacobite army under the command of Patrick Sarsfield from Ireland to France, as agreed in the Treaty of Limerick on October 3, 1691, following the end of the Williamite War in Ireland. More broadly, the term "Wild Geese" is used in Irish history to refer to Irish soldiers who left to serve in continental European armies in the 16th, 17th and 18th centuries, or even, poetically, Irish soldiers in British armies as late as the First World War.

The first Irish troops to serve as a unit for a continental power formed an Irish regiment in the Spanish Army of Flanders in the Eighty Years' War in the 1580s. The regiment had been raised by an English Catholic, William Stanley, in Ireland from native Irish soldiers and mercenaries, whom the English authorities wanted out of the country. (See also Tudor re-conquest of Ireland) Stanley was given a commission by Elizabeth I and was intended to lead his regiment on the English side, in support of the Dutch United Provinces. However, in 1585, motivated by religious factors and bribes offered by the Spaniards, Stanley defected to the Spanish side with the regiment. In 1598 Diego Brochero de Anaya wrote the Spanish King Philip III:

"that every year Your Highness should order to recruit in Ireland some Irish soldiers, who are people tough and strong, and nor the cold weather or bad food could kill them easily as they would with the Spanish, as in their island, which is much colder than this one, they are almost naked, they sleep on the floor and eat oats bread, meat and water, without drinking any wine."

The unit fought in the Netherlands until 1600 when it was disbanded due to heavy wastage through combat and sickness.

Following the defeat of the Gaelic armies of the Nine Years' War, the "Flight of the Earls" took place in 1607. The Earl of Tyrone Hugh O'Neill, the Earl of Tyrconnell Rory O'Donnell and the Lord of Beare and Bantry, Donal O'Sullivan, along with many chiefs and their followers from Ulster, fled Ireland. They hoped to get Spanish help in order to restart their rebellion in Ireland, but King Philip III of Spain did not want a resumption of war with England and refused their request.

Nevertheless, their arrival led to the formation of a new Irish regiment in Flanders, officered by Gaelic Irish nobles and recruited from their followers and dependents in Ireland. This regiment was more overtly political than its predecessor in Spanish service and was militantly hostile to the English Protestant government in Ireland. The regiment was led by Hugh O'Neill's son John. Prominent officers included Owen Roe O'Neill and Hugh Dubh O'Neill.

A fresh source of recruits came in the early seventeenth century, when Roman Catholics were banned from military and political office in Ireland. As a result, the Irish units in the Spanish service began attracting Catholic Old English officers such as Thomas Preston and Garret Barry. These men had more pro-English views than their Gaelic counterparts and considerable animosity was created over plans to use the Irish regiment to invade Ireland in 1627. The regiment was garrisoned in Brussels during the truce in the Eighty Years' War from 1609–1621 and developed close links with Irish Catholic clergy based in the seminary there, creating the famous Irish Colleges — most notably, Florence Conroy.

Many of the Irish troops in Spanish service returned to Ireland after the Irish Rebellion of 1641 and fought in the armies of Confederate Ireland - a movement of Irish Catholics. When the Confederates were defeated and Ireland occupied after the Cromwellian conquest of Ireland, around 34,000 Irish Confederate troops fled the country to seek service in Spain. Some of them later deserted or defected to French service, where the conditions were deemed better. At the time of the Napoleonic Wars there were still three Irish infantry regiments in the Spanish army: Irlanda (raised 1698); Hibernia (1709); and Ultonia (1709). However in the later years of the existence of these units only the officers were Irish or of Irish descent, the men being predominantly Spanish or other foreigners. All three regiments were finally disbanded in 1815.