Fifty years ago, on Jan. 15, Nigeria’s civil war ended. Fought between the country’s southeast region, which seceded and called itself Biafra, and the rest of the country, which Britain supported and armed, the war was brutal. Over a million people died during three years of conflict. After being starved into submission by a blockade, the Biafrans surrendered and their leaders promised to be “loyal Nigerian citizens.”

Half a century later, the war’s legacy continues to hold Nigeria captive. It simultaneously brings the country together and pushes it apart.

In the early aftermath of the war, the country appeared to be unified. Despite the war’s shocking human tragedy, reconciliation was remarkably rapid. War and partition ironically created a consensus: The country, now united, should never be allowed to break apart again. The government declared a general amnesty for wartime combatants, refused to punish either those who led the secession or those who suppressed it and did not give medals to any soldiers who fought in the so-called Brothers’ War.

The country was re-engineered to prevent another secession. To find a way for Nigeria’s more than 250 ethnic groups to live together peacefully, the country was split into 36 states, most of which coincided with the location of a major ethnic group. The federal government, whose power was increased, provided the states with funds — which created a financial deterrent against secession.

Postwar leaders found another way of building national unity: the concept of “federal character.” A new Constitution required the composition and conduct of government to “reflect the federal character of Nigeria.” Its purpose was to ensure that no ethnic group would monopolize leadership of the government or be excluded from national economic and political opportunities. Still in place today, it in effect operates as one of the world’s biggest affirmative action schemes. Nigerian law even bans political parties if they adopt names, logos or mottoes with ethnic, geographic or religious connotations, or if their membership does not satisfy constitutional diversity requirements.

But these efforts to ensure national unity, however well intentioned, froze Nigeria in time-bound assumptions about what the country should look like. The postwar desire to prevent another secession generated a near obsessive ethnic micromanaging of national life — and created a nation that exists almost simply to share money and jobs. “Federal character” became the most controversial two words in Nigeria’s Constitution. An ethnic quota regulates almost every facet of public life: Admission to the government and the Civil Service, schools and universities, the military and the police is decided by regional origin.

Rather than working as a glue for unity, the fixation on ethnic sharing of national opportunities and resources made Nigerians more aware of their ethnic differences. Resentment rose in parts of the country badly served by the quota system. The irony is plain: To prevent the recurrence of a war fought at least partly on ethnic lines — Biafra was populated mainly by the Igbo ethnic group — Nigeria’s rulers solidified ethnic identities.

What’s more, instead of ensuring the country’s unity, the postwar settlement generated conflict. For much of the past 20 years, Nigeria’s military has been engaged in fighting insurgencies in the north and south of the country. The long-running insurgency in the oil-producing Niger Delta region, in the country’s south, has indirect links to the postwar settlement. By controlling revenues from the country’s lucrative petroleum industry and requiring them to be shared nationwide, the federal government stripped control from local communities.

The postwar settlement created another profound division: between Nigeria’s people and their political leaders. For much of the past 50 years, Nigeria has been governed by the soldiers who won the war. For three decades, the form of rule was direct: Nigeria was under military dictatorship. But the passage to democracy, undertaken in 1999, did not dispel the military’s hold on the country. Military rulers were reluctant to cede power to, or accept the demands of, civilian opposition groups that called for national restructuring and the devolution of power to state governments. Instead, the generals engineered what the civilian opposition criticized as an “army arrangement” and ceded power to one of their own — the retired general Olusegun Obasanjo, to whom the Biafran Army surrendered in 1970.

The generals’ reluctance to dismantle the postwar system mummified Nigeria, ushering in a kind of gerontocracy. In a country whose population is overwhelmingly young — two-thirds are under 30 — the distorting effects of such generational asymmetry cannot be understated. Even now, the officers of the civil war continue to rule the country. Muhammadu Buhari, a 77-year-old retired major general, is Nigeria’s current president.

Even one of the seeming successes of the postwar period — the speed with which the country moved on — brought difficulties. In the rush to “forgive and forget” after the war, Nigeria skipped key questions about its purpose, its form and its destiny. There was no official narrative of what happened, nor an appraisal of lessons learned from it.

The absence of official accounts led others to fill the void. Denied the chance to articulate their grievances through formal channels, such as a war crimes trial or a truth and reconciliation commission, the Igbo ethnic group, which spearheaded the secession, has richly chronicled its suffering and sense of injustice. Barely a year goes by without an Igbo author publishing a book about the war. One of the most successful African novels of the past 15 years, “Half of a Yellow Sun” by Chimamanda Ngozi Adichie, tells the story of the civil war from a distinctly Biafran perspective.

The history written not by the war’s winners but by its losers has become yet another means of division. The parts of the country that won the war want to stop talking about it — and view the Igbos, with their memorializing habits, as something of a fifth column. Ironically, the Igbos, who may be Nigeria’s most widely dispersed ethnic group, are found in every corner of the country. With substantial nationwide business and trading interests, polyglot and intermarried with many other groups, far from a group set on secession, they show how much Nigeria has changed in the past 50 years.

But Nigeria remains haunted by the ghosts of its civil war. It simply stopped the war without addressing its root causes. And by refusing to discuss the war’s legacies, the country’s rulers bred a deep, dangerous disenchantment.

The war may have ended 50 years ago, but its effects are far from over.

• Max Siollun (@maxsiollun) is a Nigerian historian and the author, most recently, of “Nigeria’s Soldiers of Fortune.”