The only consensus that exists about how and why certain cities are appointed national capitals is that there is no common narrative.
Each one has its own story based on the history of its nation.
This disappointing conclusion is balanced by the quixotic range of capital cities that are on display as a result.
Of the world's ten biggest cities, just five are national capitals.
At the other end of the scale, the 10% of Nauru's population that lives in Yaren makes it the world's smallest national capital with a mere 1,100 inhabitants.
Of more interest to futurologists and investors alike, though, are modestly small capitals of large and growing countries. Here follows a rundown of three such urban centers to watch in the coming decades.
Despite being Nigeria's sixth most populous city, Abuja is one of the world's smallest capitals in relation to its country's population, at just 0.45% of the total, or 780,000 people.
More importantly, this has made Abuja the fastest-growing city in the world between 2000 and 2010, expanding by 139%, according to the UN.
Since 2015 this is thought to have slowed to a mere 35% per year, making it the fastest-growing city in Africa, a continent that specializes in such things. Needless to say, this yields untold challenges and opportunities for the city, which has been drawing the attention of intrepid investors from all corners of the business world.
The city was built for purpose in the 1980s by a consortium of US construction companies and replaced gridlocked, smoggy Lagos as Nigeria's capital in 1991.
The government had been looking for an alternative capital since independence, and Abuja was earmarked in the 1970s mainly for its ethnically and religiously neutral position at the center of the country, from where it was hoped economic opportunity would be spread to Nigeria's restive interior.
The plan worked.
Abuja's wider metropolitan area has since settled some 6 million migrants, both internal and from Nigeria's ECOWAS trading partners to the West.
Like any capital city, Abuja's fate is tied to that of its country, and the fact that the median age of Nigeria's vast 191 million population is just below 18 makes future planning a daunting task. The World Population Review expects the population to grow to 300 million by 2036, by which time Nigeria will have Africa's largest economy, as well as its largest population. Abuja looks set to continue to be the city most affected by wider changes in the country.
The only other significant capital city that boasts an even smaller population relative to its country's total population is Washington DC, which is home to a staggeringly small 700,000 people, or just 0.21% of US citizens.
It stands as the 20th largest city in the country.
Despite being outshone by commercial and cultural capitals like New York or San Francisco, and in spite of historical restrictions on its physical growth, Washington's wealth and population are forecast for steady expansion in the near future.
The city's rough location was set as part of a compromise between Alexander Hamilton and Thomas Jefferson, but was founded by its namesake, George Washington, in 1791 to house all 131 employees of the Federal Government.
Because it was founded by the US Constitution under exclusive jurisdiction of Congress, Washington is not technically part of any US state.
The District of Colombia's odd shape was originally conceived as a square standing on one end, straddling the Potomac River and built on land donated by the states of Maryland and Virginia. When Virginia's land was returned by Congressional decree in 1846, DC was condemned to the awkward form it takes to this day, as well as to a very limited area of just 177sqkm.
Despite this, the District of Colombia's metropolitan area has recently grown to house around 6 million people, while commuters from surrounding states swell Washington's daytime population to over 1 million.
Washington DC's dynamic, cosmopolitan population has increased by 100,000 every decade since 2000, which had followed six consecutive decades of contraction.
Residents are also younger and wealthier than their average fellow American.
If this pace continues, Washington DC will be combining developing-world rates of population growth with first-world capabilities, presenting investors with opportunities across a range of sectors.
Recent improvements to the city's historically high crime rates will be something to watch going forward.
Weighing in with just over 1 million inhabitants, Pakistan's administrative capital Islamabad is no lightweight, at least not until you realize that it is only the 9th largest city in the country.
Following commercial hotspots such as Gujranwala and Peshawar, Islamabad is by no means the largest city in Pakistan.
But the 0.48% of Pakistanis who live in Islamabad have the financial and intellectual clout to set their hometown as the scene of much future development and investment.
Designed by a group of Greek architects, Islamabad was unveiled as the new seat of government in 1960, signifying a break from colonial Karachi, which had improvised as Pakistan's capital since the establishment of independence from India in 1947.
Although landlocked, the Pothohar Plateau was a traditional crossroads between Pakistan's peoples, and was more accessible from around the country, not least from the disputed Kashmir region in the north and Karachi in the south.
A 1998 census revealed Islamabad's total migrant population to be 1 million—so almost everyone—with the majority of them coming from Punjab province.
With 38% of inhabitants under the age of 15 and an unusually high literacy rate of 88% and with Pakistan's population projected to balloon from 197 million today to 245 million by 2030, Islamabad looks set to function as base camp for the gradual unleashing of Pakistan's economic potential.
That relies on the country getting to grips with the corruption and security issues that have long put investors off Islamabad's grand plans.