For nearly three centuries after the Reformation, Glasgow’s religious conflicts were Protestant family quarrels; Catholics were too few to persecute. The famine-driven Irish immigration of the nineteenth century changed the arithmetic entirely: by mid-century a substantial share of the city was Catholic and Irish, poor, crowded into the worst housing — and resented. Onto Scotland’s old anti-Catholic reflexes was grafted an ethnic division, and Glasgow acquired the sectarianism that would shadow its next hundred and fifty years. (Irish Protestant immigration, substantial in itself, brought the Orange tradition along the same sea routes.)
The division organised itself thoroughly. Orange lodges and Hibernian societies marched their calendars; whole trades and firms operated informal religious bars — ‘What school did you go to?’ serving as the polite form of the question — with Catholics long excluded from swathes of skilled work, and separate Catholic schooling (state-funded from 1918, to Protestant fury at the time) giving the divide an institutional spine. In the 1920s and 30s it turned openly political and ugly: militant Protestant parties won council seats, and razor-gang street violence often ran along the same seam, as the Crime & Justice section records.
Its most visible theatre was football. The Old Firm rivalry — treated fully in the Football section — became the fortnightly performance of the division, complete with flags, anthems and, for most of the twentieth century, Rangers’ unwritten bar on Catholic players; the fixture’s riots and tragedies belong to that same history.
The retreat, when it came, came from underneath: the collapse of the industries whose workplaces enforced the bars, slum clearance’s scattering of the old territorial communities, intermarriage rising past the point of remark, and the general secularisation that emptied the pews on both sides of the divide. Landmarks piled up quietly — the ecumenical decades, Mo Johnston’s 1989 signing, papal visits passing off as civic occasions — until sociologists could argue, plausibly, that the average Glaswegian’s life contained no sectarian dimension at all.
Not dissolved, though: marching seasons still require policing, the songbooks have not been fully retired, and legislators have attempted (and repealed) laws against football-linked bigotry within living memory. Glasgow treats its sectarianism now much as it treats its rain — a diminished thing it refuses to pretend is gone; and the honest telling of how it grew is part of how it goes.