In the run-up to the landmark, opinion is split between those who think amalgamation has been a boon and others who consider it the first step in the creation of a still-failing state.
Writer Adewale Maja-Pearce described Africa's most populous nation as one "imposed by the colonialists who dreamt up the fiction which has now become the nightmare we are all struggling to escape".
The most pressing question now is whether to continue trying to "make it work", the International New York Times columnist told AFP.
Nigeria's first step towards independence in 1960 was taken on New Year's Day 1914 at a ceremony outside a courthouse in the southern city of Lagos.
The British rulers hoped that trade would be boosted by uniting the economically faltering north with the more prosperous south.
But the primarily commercial move, as with others in Britain's then-global empire, also fused an array of people divided by custom, language and, perhaps most importantly, faith.
By the start of the 19th century, northern Nigeria, where the Fulani-Hausa ethnic group was dominant, had become a caliphate, controlled by a structured network of Islamic theocrats.
The south meanwhile consisted of scores of ethnic groups and a loosely-structured maze of leaders and tribal chiefs.
That made it a far tougher territory for the British to manage, said Ed Keazor, a historian consulting the Nigerian government on the centennial celebrations.
For Frederick Lugard, Britain's high commissioner of northern Nigeria and later the first governor-general of the amalgamated colony, the north "worked better", added Keazor.
Lugard "was an autocrat", Keazor said. "The emirs' (Muslim rulers) style suited his own style."
But lacking cash crops, the north by 1912 needed subsidies from London to meet its administrative costs.
Lugard hoped his amalgamation project would raise profits by streamlining the management of the colonies with him at the top.
With war in Europe brewing, London decided to give the idea a try.
"Today, Nigeria enters on a new stage of progress," Lugard said outside the Lagos supreme court building on the first day of 1914, according to a text provided by Keazor.
"We all join in earnest hope that the era now inaugurated will prove, not only a departure in material prosperity, but also... increase the individual happiness" of the Nigerian people, he declared.
Amalgamation proved an early success for Britain, according to several accounts.
The north's economy improved, backed by a surge in cotton production and better access to the ports lining Nigeria's southern coast.
After the end of World War Two in 1945, Nigeria was split into three geopolitical zones: the mostly Hausa north, the Yoruba-dominated west and the east, where Igbos were the majority.
The two southern regions had by then become majority Christian.
But in the late colonial period, "political combat most often boiled down to a three-way struggle", the International Crisis Group said.
On the eve of independence, perhaps aware that its amalgamated colony had become a powder keg, "the British agonised over whether the country should be split in two parts -- a Christian south and Muslim north", wrote David Cook, a specialist in radical Islam at Rice University in Houston, Texas.
That did not happen but the new nation did fracture within its first decade.
The 1967-1970 Biafra civil war began after the Igbo-led region, alleging their tribesmen were being massacred in the north, tried to secede.
In the three decades after the war, Nigeria was mostly led by military dictators from the north in an era that saw the country's huge oil resources squandered through corruption.
Elsewhere, sectarian violence in the "Middle Belt" dividing north and south has killed 10,000 people since 1992, Human Rights Watch reported this month.
More than four thousand people have died since 2009 in an insurgency waged by radical Islamist group Boko Haram.
The Islamist violence has not spread below the Middle Belt but has inflamed anti-northern sentiment in the south.
"It is only oil that has kept us together," said Maja-Pearce.
Petro-dollars have been used to smooth out political rivalries, pacify rebels and generally "patch up" conflicts which could have threatened Nigeria's unity, he added.
The People's Democratic Party, which has led the country since 1999, has an unwritten rule to rotate its leaders between southern Christians and northern Muslims, aiming to ease regional tensions.
For Professor Dapo Thomas of Lagos State University, politicians who still fixate on and exploit regional rivalries "are the ones who made a mess of amalgamation".
"I believe the amalgamation was the best thing to have happened to Nigeria," he told AFP.
Already home to the continent's biggest population, with an estimated 170 million, Nigeria may soon boast Africa's largest economy.
Thomas attributed that -- and the country's growing political and cultural clout -- to amalgamation.
"All we need is the spirit of accommodation... and a leader who will explore the positives in our diversity," he added.