The Battle of the Boyne was a turning point in the Williamite war in Ireland between the deposed King James II of England and VII of Scotland and his son-in-law and successor, William, for the English, Scottish and Irish thrones. It took place on July 1, 1690 just outside of the town of Drogheda on Ireland's east coast. Though not militarily decisive, its symbolic importance has made it one of the most infamous battles in British and Irish history and a key part in Irish Protestant folklore. As a consequence of the adoption of the Gregorian calendar, the battle is now commemorated on July 12. But is widely remembered as a decisive moment in the struggle between Protestant and Catholic factions in Ireland. Twenty-six thousand, mainly Irish and French troops under King James, fought against the thirty-six thousand Dutch and English soldiers of King William. On the first of July 1690 near Oldbridge, then a small village five miles East of Drogheda, King William of Orange and King James II fought in one of the most well-known battles in Irish history. Prior to the battle King James' army had marched through Drogheda and they took up position on the northern face of Donore hill just south of the river. Late in the evening of the first of July the Williamite army, better trained and equipped, began to take control. King James and his army retreated to Dublin through the Pass of Duleek. They were finally defeated at Aughrim in 1691. That defeat decided the fate of Catholicism in Ireland with the introduction of the penal laws.
The war was a sectarian and ethnic conflict, in many ways a re-run of the Irish Confederate Wars of 50 years earlier. For Irish Jacobites, the war was fought for Irish sovereignty, religious toleration for Catholicism and land ownership. The Irish Catholic upper classes had lost almost all their lands after the Cromwell's conquest and had also lost the right to hold public office, practice their religion and to sit in the Irish Parliament. To these ends, under Richard Talbot, 1st Earl of Tyrconnell they had raised an army to restore James to his throne after the Glorious Revolution. By 1690, they controlled all of Ireland except for the province of Ulster. Most of James II's troops at the Boyne were Irish Catholics. Richard Talbot, 1st Earl of Tyrconnel (1630 – 14 August 1691), the youngest of sixteen children of Sir William Talbot, Bart., of Carton, was descended from an old Norman family that had settled in Leinster in the eleventh century. Like most Old English families in Ireland the Talbots had adopted the customs of the Irish and had, like the Irish, adhered to the Catholic faith. He married Katherine Baynton in 1669. Talbot later married Frances Jennings, sister of Sarah Jennings (Sarah Churchill, Duchess of Marlborough). He was also known by the nickname "Mad Dick" Talbot. During the Irish Confederate Wars that followed the Irish Rebellion of 1641, Talbot served in Confederate Ireland's Leinster army as cavalry cornet or junior officer. He was taken prisoner by the Parliamentarians after the battle of Dungans Hill in 1647, but was ransomed back to his own side. In 1649, he also survived the Cromwellian sack of Drogheda, escaping from the garrison before it was massacred. Shortly after this, he fled Ireland, to join his fellow defeated Royalists in France.
After Boyne River 1690 Mass migration of 14,000 followed; this is known as the Flight of the Wild Geese. Irish to France or New France.
After the "Flight of the Wild Geese" in 1691 and the institution of the Penal Laws, which mitigated against Catholic ownership of land, commercial business, or even a basic education, most of the lands of the ancient Gaelic overlords were held by Protestant landlords of English descent. These landlords neither spoke Gaelic nor understood the ancient customs and folkways of their tenants. This led to much hostility between peasants and gentry which continued in some areas of Ireland up to the present century. Most of the lands of Dysert (which for centuries belonged to the Diocese of Killaloe) went to the family of Synge which had been involved in ecclesiastic affairs in the Established Church since the 1670s. After the Cromwellian and Williamite wars in the latter half of the 17th century, thousands of Irishmen emigrated to France where they were guaranteed service in the army of King Louis. The O'Deas were no exception. Two sons of Michael O'Dea of Dysert, James and Donough, followed their uncle James into the Irish Brigade. It rose steadily in the parish of Dysert from about 2,000 people in 1690 to over 7,000 by 1840. The great Potato Famine resulted in over one million deaths in Ireland from starvation and disease, and the emigration of over one million people to Britain, the United States of America, and Australia.