So let's talk about all the various types of rebellion that occurred in the medieval world.
We've already examined the types of popular revolution that happen when food prices are shaken, but there are other forms of rebellion and replacement of the political order than merely the overhauling revolution.
There are several things that lead to rebellion, a laundry list of factors as it were. These include but are not limited to:
(a) A sizable intelligentsia unable to access political efficacy.
(b) Insecurity in food supply or income.
(c) In the medieval context of polities that are reliant on personal charisma, personal disagreements or other forms of friction between individuals.
(d) Growing pains after an attempt (successful or not) at centralization.
Several of these can be consolidated into a single element, mainly: weakness of the central authority. The reason for this is, of course, that someone in the kingdom always has a better idea at how things should be run, or a more legitimate claim to the title, or just more ruthlessness. Rebellion and insurrection are in fact native forces that simply wait for the center to fail. They are the entropic principle of a kingdom (or, in modern terms, a state). As wood rots and the arrow of time flies ever forward, the death of the kingdom is already contained within it, waiting for release.
The most common types of rebellion in medieval polities are, of course, those that focus on one of the following issues:
(i) inheritance grievance
(ii) centralization grievance
(iii) religious grievance
(iv) interpersonal tension
All of these issues require an alternative pole to the king to coalesce and take form. This can be the king's paternal uncle, for example, or a brother or son. Paternal uncles were particularly dangerous in the very early middle ages, often killing their brothers' sons in order to take over. Brothers can be equally treacherous—take, for example, the unification of Frankia that relied upon Charles packing his son off to the monastery and fortuitously watching Carloman die.
We can take an archetypical rebellion as a pattern, namely the infamous Anarchy that occurred during the realm of King Stephen. Now, this analysis isn't quite as rigorous as, say, a historical book on the subject. I may miss some of the root causes of the rebellion, but I can at least give the outline.
King Henry, who succeeded William Rufus, who succeeded William the Conqueror, had a son named Henry and a daughter named Matilda (or Maude). Maude was married to the Holy Roman Emperor, who later died, and then remarried to Geoffrey of Anjou. When Henry Adelin, King Henry's son, died in the sinking of the White Ship, King Henry demanded oaths of all his barons that they would crown the so-called Empress Matilda queen after his death.
However, he died fighting in Normandy and his cousin, Stephen of Blois, announced that on his deathbed Henry had named him the heir, following in a long tradition of truths as told by his ancestors, like William the Bastard (that's sarcasm, kid).
Anyway, he rushed to London and got himself proclaimed king. However, Maude still had a number of followers among the barons who grudgingly accepted his kingship. Her half-brother, Robert Earl of Gloucester (also Henry's bastard), began sowing the seeds of rebellion early in Stephen's rule and drawing her loyal followers to him.
When the time was right, Robert went into open revolt, and David, King of Scotland (a perennial thorn in Stephen's side) aided him by invading. David had already invaded once, as he was Matilda's uncle (and was probably using that chance to make a political grab of land in the north of England). Notice this theme: Matilda, the pole of legitimizing succession, gives David a claim to invade. Whether or not he really wanted Matilda to succeed her father is open to debate; though, that would also be wise, as it would create a loyal ally to his south.
Stephen was having troubles with Wales and his coffers were emptied out when Robert rebelled. Whether it was the chance Robert needed or whether Stephen appeared weak and ineffectual, thus driving more lords into Robert's arms, is uncertain. Whatever the reason, as soon as the center was weak enough, the revolt began.
Matilda was its figurehead, but Robert was its heart. He could never be king—his illegitimacy prevented it. Matilda, however, was a convenient figure to rally around.
In the unfolding of the Anarchy, we can see at play the interpersonal relationships of powerful medieval figures leading the road to war. This is a problem of (i) and (iv), triggered by a general weakness in the central polity due to raiding and expenditure of silver.