A friend of mine once told me (a paraphrase) that all of history can be divided into three phases: 1) someone is in charge - this is usually peace; 2) someone wants to be in charge - this is usually war or tyranny; 3) no one is in charge - this is chaos, anarchy, and war. Because of this, I try to figure out what power structures look and act like, how they relate to each other, and what they actually mean.
The first thing i had to do was be very careful about the word 'feudalism'. One scholar I read stated (another paraphrase) ''Feudalism' is a term only used to describe systems long after they were begun or even ended. The popular idea of what the term meant is so broad and ill-defined that if you accept it then all people at all times everywhere were, are, and will always be in a feudal system'.
The Saxons in England had kings ( I am descended from 2 or them), but the term was very little like we imagine. In a number of cases there were kingdoms with three kings - there was a man called King because his father was a king, a man called King because his sonless brother was a king, and a man called King because the warriors would actually follow him into battle. This dynamic, fluid understanding of what a king was contrasts sharply with the views of 15th Century France where the king was king by divine right and through purity of blood and considered the absolute ruler of all of France.
Unless you asked the Duke of Burgundy for his opinion, of course.
Various Chinese emperors were likewise seen as divinely appointed and favored - as long as the famines were dealt with, invaders, kept out, and the taxes not too high, of course. otherwise the peasants might stage another revolt, end another dynasty, and start another new dynasty. And this new emperor would probably be just as incapable of dealing with a corrupt civil service and most others were....
The Japanese are in a unique position - their imperial line is unbroken for over 2,500 years! Of course, while the emperor has always been there there were often others ruling 'in the name of the emperor', meaning the emperor may have been far from in charge.
Just within Medieval Europe during the "Feudal Period" there were a dizzying range of types of leadership. There were [deep breath]: effectively independent robber barons on the edges of the Holy Roman Empire; the confederation of merchant and trade guilds of the Hansa which had its own armies, navies, and colonization efforts; Imperial Free Cities run by local oligarchies/plutocracies; a large region ruled by a religious military order of knights; cities or nations ruled by an archbishopr or cardinal of the Church; regions dominated by clan and tribal affiliation (effectively extended families); and a parliament in Iceland.
And an empire. And lands conquered and colonized by invaders from a distant land. And more, beside.
The reason that this matters to world building is simple - in the Real World either there is already someone in charge or there is no one in charge: the alternative to someone already claiming it is that the land you are on is howling wilderness. I think it is safe to assume that a game world would be similar. The characters will be forced to deal with these power structures every day unless they remain in the wilderness!
What if the elves, or at least the local ones, have a Saxon-like arrangement? Let's say the players need to cross the elven Kingdom of Argalen to get to the dragon's lair. They meet with a group of elves, talk for a while, pass around some wine and gold coins and meet with King Maeglin. More wine and gold later and, well, the King has given them permission to pass through - great! Next day the party goes on and soon enough smack into some elves that demand a toll. The party explain that King Maeglin gave them free passage. These elves laugh heartily, toss the 'free passage medallion' Maeglin gave you into a box full of duplicates, explain Maeglin is 'only' the son of the last king, and tell you King Edhelcu demands 20% of the wealth of all non-elves crossing through is kingdom. The party grumbles, coughs up the cash, and keeps going. Two days later they are invited at arrow point to meet with King Finan and explain why they are trespassing in his kingdom....
Of the party's home base is an Independent City? They are listed as 'visitors' and must pay a yearly tax, face higher exchange fees, etc. To get out of this they must be sponsored by an existing citizen and buy citizenship, a long and expensive process. But even after doing that they find that the city council is only open to the Big Families, the 7 richest merchant families in the city.
On a much grander scale these decisions are going to impact the campaign tone a great deal - a tyrannical plutocracy surrounded by robber barons, grasping merchant leagues, and hordes of tribal humanoids is going to have a very different tenor and morality from a paladin-run crusader state bordering an invading colony and backed by bucolic Late Medieval French clones....
So when thinking about world beulding remember - there is a lot more out there in the Real world to draw from than Hollywood Vikings and Hollywood Princesses!