Irish neutrality in the Second World War cannot be understood without reference to the overwhelming influence of the legacy of the independence struggle on Anglo-Irish relations, on Irish foreign policy considerations, and on the Irish public's perceptions of where the new state's interests lay and who its natural enemies were.

Independent Ireland was the product of the Anglo-Irish treaty of 6 December 1921, under which twenty-six counties of the 32-county island were recognised as a separate dominion within the British empire. The six counties in the north-east of the island had already been separately established as the self-governing province of Northern Ireland, an integral part of the United Kingdom. As Irish separatism had long regarded the national territory as encompassing the entire island of Ireland, and as Northern Ireland contained a large and alienated nationalist minority, many in the new Irish state regarded partition as an unnatural evil, Britain's last malign act before she reluctantly ceded qualified independence to the rest of the country. As head of successive governments from 1932 until 1948, Eamon de Valera constantly characterised partition as the greatest blight on Anglo-Irish relations (although after 1923 he always sought to channel nationalist resentment against it into conventional political channels).

From the first day of its existence, independent Ireland adopted a policy of military neutrality. Although the independence struggle had seen some flickers of ambition for a large-scale military and naval establishment, by the time the state came into being these had evaporated.