Answer extracted from the The Rest Is History podcast — listen to the full episode below.
What was the population of Ireland at the start of the 20th century and how was it divided religiously?
In 1900, Ireland was home to approximately 4.5 million people, all subjects of the United Kingdom. Three-quarters of the population were Catholic, while one-quarter were Protestant—a religious fault line that would shape conflict for generations to come.
This stark religious majority masked a critical geographic distinction. While Catholics dominated the island as a whole, Protestants were heavily concentrated in the northeastern province of Ulster, particularly around the industrial city of Belfast. This concentration created a region fundamentally different from the rest of Ireland in both religious makeup and economic character.
The census figures reveal the foundation of what would become one of the defining tensions of modern Irish and British history. Catholics, seeking independence and home rule, vastly outnumbered Protestants across most of the island. Yet in Ulster—especially in Belfast's shipyards and industrial heartland—Protestants formed the majority and held enormous economic and political power, a reality that would fuel decades of sectarian division.
Just twelve years later, in 1912, almost half a million Ulster unionists signed a covenant led by Sir Edward Carson, pledging to resist Irish home rule by all means necessary. This covenant would echo far beyond its signing, setting the stage for the partition of Ireland and the creation of Northern Ireland—a decision made partly to protect the Protestant-majority population of Ulster from being incorporated into a Catholic-dominated Irish state.
The geography of faith and power
The religious division was not merely a matter of statistics—it mapped directly onto economic and political power. Belfast's industrial boom in the late 19th century had been built largely on Protestant capital and Protestant labor, creating a prosperous enclave with its own identity, separate from the agricultural and less developed Catholic regions of the south and west.
This economic disparity reinforced communal identity. The industrial city of Belfast became a symbol of Protestant Ulster's distinct character, a place where shipbuilding, linen manufacturing, and engineering created wealth and employment. For Protestants in Ulster, the prospect of being ruled from Dublin by a Catholic majority felt like economic and political subjugation.
Yet for Catholics across the island, the sheer numbers—three-quarters of the population—gave them confidence that democratic self-rule would finally answer their long struggle for independence. What emerged from this collision of demographics and power was not consensus but partition, a division that froze these religious lines into political borders. The episode explores how this 1900 census became the starting point for a century of conflict.
See also
What was the 1935 Belfast rioting and how serious was it?
In 1935, massive rioting erupted in Belfast with gun battles and snipers on buildings, requiring British troops with armored cars to clear the streets. Eleven people were killed, around 100 injured, and approximately 2,000 were driven from their homes.
What was Sir James Craig's position on Northern Ireland as a Protestant state?
Sir James Craig, the first Prime Minister of Northern Ireland, stated explicitly in the 1930s that he wanted Northern Ireland to be a Protestant state for a Protestant people, mirroring the South's claim to be a Catholic state.
What was the IRA's S-Plan bombing campaign in Britain in 1939?
In January 1939, the IRA launched a sabotage campaign called the S-Plan against Britain, planting bombs in major cities including London, Birmingham, Bristol, and Liverpool to destabilize the British economy and government.