While the Irish national identity took another millennium to undergo the same formational the English principally defined itself by creating a dynamic between two peoples whose core identities were, in large part, mutually exclusive.

October 26, 2018, marked the 1,119th anniversary of the death of the emblematic Alfred the Great, the ninth-century Anglo-Saxon king best remembered in history as the first to exert his lordship over the entirety of the territory now called England.

The events that led to his reign are murky and little understood, but they provide key insight into the deep roots of both English and Irish national identities, both of which defined themselves against each other and which necessarily formed the foundation of the modern Anglo-Irish relationship.

The Province of Britannia rested on the outer edge of the Roman Empire's northwestern region. Despite its relative isolation, the colony achieved a respectable degree of prosperity, though this made it subject to frequent raids from Celtic pirates stationed just beyond the horizon of Empire.

Britannia's access to the extensive imperial network and its deep supply of resources practically guaranteed that these raids were usually no more than an incessant annoyance. But when Rome faced widescale disruptions beginning in the third century, its attention was inevitably drawn away from Britannia and towards the areas of greatest geopolitical significance.

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Britannia faced a local crisis simultaneous to Rome's growing difficulties. In 367 AD, a loose alliance of Celtic warrior bands launched a full-scale assault on the province. Flowing in seemingly never-ending waves from Scotland and Ireland, Britons found themselves unprepared and overwhelmed. Though the technological and organizational superiority of the support Rome eventually mustered ensured the protection of the colony, the event made clear that Britannia's defense absolutely depended on the will of Rome.

Moreover, it ingrained into the fabric of proto-British society the notion of the Celts as a powerful and ruthless threat against whom a constant and institutionalized sense of vigilance was required.

Small-scale plundering littered the decades thereafter, but as the Roman metropole wilted and the Empire began to crumble around it, Celtic pirates again felt emboldened to intensify their activities. Increased Celtic attacks on the Britannic coastal defense system coincided with waves of Germanic migration along the continental frontier, stretching Rome's resources to unprecedented extremes and ultimately forcing it to abdicate its responsibilities in Britannia and abandon the population that remained therein.

Occurring alongside these events, Germanic seafarers originating in what is now Denmark and northern Germany fled the continent and migrated westwards towards Britain. The Anglo-Saxons--as the settled peoples were known- entered into a cesspool of conflict, but they were no less eager to seize their spoils.

The native Britons recognized that they could no better defend against the Celtic raids than they could absorb the Anglo-Saxon migrations. They resolved to form a military-political alliance with the new arrivals, evidently considering the threat posed by their traditional Celtic foes far more menacing.

They ceded swathes of territory along the southeastern portions of Britain in exchange for military cooperation and protection. The Anglo-Saxons' ability to protect the British communities established their authority on the island and ultimately won them the allegiance of other exposed bands stretched across the former colony.

Anglo-Celtic relations stabilized by the beginning of the eleventh century as Anglo-Saxon kings turned increasingly towards state-building and Celtic chieftains focused more on their internal rivalries, both of which occurred in the face of the Viking threat from abroad.

Nonetheless, the Anglo-Saxons' chaotic inception manifested the foundational quality of the earliest form of English identity. Though one should not misconstrue this to mean anything akin to our modern sense of nationalism, the earliest indications that medieval Anglo-Saxons felt that they composed a single people defined by a set of shared characteristics were implicitly foiled against those exhibited by the neighboring Celtic peoples.

Feelings of collective identity almost always emerge against the backdrop of a well-defined 'other.' This is especially true for ethnic identities, whose 'other' is readily identifiable as a neighboring group with a different language, culture, and history, and who usually represents a threat of some kind.

The perception of a common threat causes the perceived victims to form alliances with individuals with whom they share certain cultural characteristics in order to preserve what they perceive as common interests. It was these same processes which enticed Anglo-Saxons to consolidate into some semblance of unity in order to gather the strength needed to defeat what they all perceived to be a common Celtic threat.

It should be said that these processes occurred neither intentionally nor consciously, but over time they did facilitate the emergence of a cohesive, if still primitive, sense of English identity.

The earliest Anglo-Saxon migrants did not depart from the continent with any overt objective, but when they arrived in Britain, they adopted almost immediately their defining purpose: to protect the island and its inhabitants from Celtic attacks originating in Scotland and (especially) Ireland.

These were the conditions on which the Anglo-Saxons were permitted to settle, and the preponderance of their earliest activities were directed towards fulfilling this purpose.

This is vital in order to understand the fundamental nature of the Anglo-Irish relationship. While the Anglo-Saxon identity developed along the same natural processes outlined in a previous paragraph, they were reinforced by a more explicit sense of who belonged, who did not, and who was meant to preserve those distinctions. Thus, not only did the Anglo-Saxons build an understanding of themselves on the basis that they were not Celts, but they also accepted that their purpose in Britain was to exclude the marauding Celt from the confines of their new territory.

These attitudes formed the core element of the Anglo-Saxon mentality, and long after the Celts no longer posed any meaningful threat to the newly-unified Kingdom of England, the sense that it was England's duty to subdue the unruly peoples of Scotland and Ireland prevailed, and it was what primarily motivated King Henry II to request approval from Pope Adrian IV in the twelfth century to authorize the first military expedition to Ireland.

Although the definitions of identity tend to ebb and flow with changing social environments, England's tendency to re-enact its ancient purpose remained the constant feature, and it was simply repurposed over the ensuing centuries to fit new circumstances.

It would take almost a full millennium for the Irish national identity to undergo the same formational processes that the English identity did in the early medieval period, but when it did, it would principally define itself against the well-established notions of Englishness, creating a dynamic between two peoples whose core identities were, in large part, mutually exclusive. By that time, the English identity had evolved into a far more dynamic and more encompassing concept, but nonetheless, these competing attitudes would form the central components of both the Republic of Ireland and the United Kingdom's attitudes regarding the other, affecting the modern courses of both states and in many ways still impacting relations between them today.

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Artist's depiction of the Battle of Brunanburh (937 AD), one of the most pivotal medieval battles between Anglo-Saxons and Celts.