This answer is informed by two things:
1. The Sword Coast Adventurer's Guide (pages 7-20)
2. Human political organizational habits of the history of RL
The Costa de la Espada as a whole is not governed as "The Costa de la Espada"
Its structure (as if there were any structure) is a fusion between the feudal period before and after Charlemagne's reign as Emperor of the Holy Roman Empire, the State model of the ancient Greek city and a nod to extra-national organizations such as the Hanseatic League of Medieval times throughout northern Europe. coastal borders (FWIW, the tradition of World of Greyhawk has a similar association called The Iron League).
City states with feudal medieval nuances
The further east there are kingdoms such as Cormyr, and further south are Amn and Tethyr, the Sword Coast region is characterized by feudal / medieval / Renaissance urban nodes separated by long stretches of wilderness areas and areas of low population density . These urban centers are a strange cultural fusion of medieval, feudal and Renaissance-style cities run by nobles. Each of them are powers in themselves. Waterdeep, Neverwinter, Silverymoon, Luskan, Baldur & # 39; s Gate, Daggerford, Mirabar, Longasaddle, Mithral Hall, Yartar and Amphail are entities of various sizes mentioned in SCAG. (SCAG, p. 43-66)
There is no king, there is no emperor. When you refer to "the law of the land", the Sword Coast does not have one. Each state of the city has its own modes of government, control and application. (Or attempts to do so). In other words, it is nothing like the world in which you live in the civilization of the 21st century.
How is the largest area of the sword coast governed?
It is not
How are laws enforced and by whom?
Locally, by local authorities.
How are officials appointed?
In the zone. Each location has its own method.
How are taxes collected?
In the zone.
You will find mentioned in the Deep dragon stroke, the Murder at Baldur's doorand other references of published adventures to taxes paid to a local authority.
Imagine that PCs join some orc attackers and kill a city; Who would come to enforce the law of the land?
There is no hard and fast answer. Either
nobody would, since it is too far away and something more pressing has
the authorities in Luskan looked after their ears (why do you think
which nobles hire adventurers in the first place?)
a local gang / armed party under the authority of a local lord
A band of adventurers / mercenaries hired by a local lord, a religious leader or a faction
If what the PCs did was atrocious enough, their attack could attract the attention of a faction or a supra-state organization such as the Lord's Alliance or the Harpers. These organizations can pool resources to track PCs and bring them to justice. (Everything depends on the DM to put it in its place, in a given game, or by the author in a given FR novel).
Commerce connects all cities.
As with normal human models of civilization, trade between the various regions and city states generates shared interests and rivalries. Trade brings prosperity and rivalry. Which leads to …
The role of factions as a mechanism in the world for political intrigue
Among the Harpers, the Alliance of the Lord, the Zhentarim, the Emerald Enclave and a variety of non-state organizations (see Knights Templar in medieval Europe / Era of the crusade for an excellent parallel) organizations with objectives and goals that are not linked to A local area act to promote its own interests in multiple areas.
- You can see a & # 39; non-state actors & # 39; similar in an organization like the
Masonic fraternal organizations (as well as conspiracy theory
versions of them) or a more political organization like Al
Qaeda or DAESH: they are not based on a country, but on a shared interest or a
shared vision of the world.
The Alliance of the Lord: an alliance instead of "government"
On page 7 of the Sword Coast Adventurer & # 39; s Guide there is a description of The Lord & # 39; s Alliance.
A confederation among the rulers of several northern settlements … in addition to providing military support and a forum for the peaceful transmission of difference, the Alliance has always acted on the principle that communities with common cause engaged in commerce have Less likely to disappear. to war with each other. By maintaining strong business ties inside and outside the alliance, the Lord's Covenant helps keep the peace.
As noted above, and according to historical ties, the link between organizations such as the Hanseatic League, commerce and "joint work where there is a common interest" is as far as a "supra-state" organization like that can go. .