The phrase is related to the enduring power of the city first as the capital of the Republic and the Empire, and later as the centre of the Catholic Church.
Historically, the major economic centre of a state or region has often become the focal point of political power, and became a capital through conquest or federation.
The modern capital city has not always existed: in medieval Western Europe, an itinerant (wandering) government was common.
They are recognized as capitals as a matter of convention, and because all or almost all the country's central political institutions, such as government departments, supreme court, legislature, embassies, etc., are located in or near them.
Many modern capital cities are located near the centre of the country, so that they are more accessible to its population and have better protection from possible invasions.
Modern examples are Berlin, Cairo, London, Madrid, Mexico City, Moscow, Paris, Rome, Jakarta, Metro Manila, Seoul, and Tokyo.
The number of new capitals in the world increased substantially since the Renaissance period, especially with the founding of independent nation-states since the eighteenth century.
The national capitals of Germany and Russia (the Stadtstaat of Berlin and the federal city of Moscow) are also constituent states of both countries in their own right.
In ancient China, where governments were massive centralized bureaucracies with little flexibility on the provincial level, a dynasty could easily be toppled with the fall of its capital.
The Ming dynasty relocated its capital from Nanjing to Beijing, where they could more effectively control the generals and troops guarding the borders from Mongols and Manchus.
The Ming was destroyed when Li Zicheng took their seat of power, and this pattern repeats itself in Chinese history, until the fall of the traditional Confucian monarchy in the 20th century.
National capitals were arguably less important as military objectives in other parts of the world, including the West, because of socioeconomic trends toward localized authority, a strategic modus operandi especially popular after the development of feudalism and reaffirmed by the development of democratic and capitalistic philosophies.