Britons will make a momentous choice on Thursday that could matter more for their future than any ordinary election. They will decide whether to remain in the European Union, as Prime Minister David Cameron has urged, or to leave, as favored by many members of his Conservative Party, including some of his cabinet ministers.

The debate around this referendum on a British exit, or “Brexit,” has been long, repetitive, emotional and sometimes vicious. It has centered on different estimates of fear — fear of economic damage from leaving versus fear of uncontrolled immigration if the country remains.

Many Britons talk of being torn between heart and head, with the heart wanting to vote for British exceptionalism and full control over the nation’s laws and borders, free of the European Union and its obligations, while the head is deeply wary of the economic risks that Britain would face if it goes it alone.

There are also deeper questions of identity — the nature of parliamentary sovereignty, the character of towns with large migrant populations, the depth of English nationalism.

But there are concerns, as well, for the fate of the United Kingdom. If Britain as a whole votes to leave, Scotland, which strongly supports remaining in the bloc, will want another referendum on independence, which could lead in time not only to the breakup of the European Union but also that of the United Kingdom.

Rarely has any nation been confronted with so simple yet consequential a choice, with young and old, rich and poor, urban and rural, north and south all given a hand in making history. – Steven Erlanger