- Peaceful protests of course happened, but they aren't documented very well.. because they were so common. Paper is cheap, as well as papyrus, wax tables and clay tablets.
- Trade sanctions: controlling trade always has been a tool of power. Who gets the tolls, the staple rights, the mill, etc. ? A step further towards war is blockading ports or trade routes.
- Sabotage was less common, because there was less infrastructure and destroying something required an army anyway due to the lack of explosives. Raiding and plundering, burning fields as a war of attrition instead of a confrontation was common practice, however.
- Propaganda: not as flexible as the modern version, but sponsoring religions/missionaries is an ancient practice. There still is pretty direct stuff, eg. the Mesopotamian kings that deified themselves, or the Egyptian Pharaohs that put up steles to commemorate their victories.
- Outright bribing was less common in times with less monetary means, but promising a count a promotion to duke if he switched allegiance from one king to another would have been considered.
1) No, they really were NOT that common. At least not on a level that was taken seriously. There is a very good reason for this. FEUDALISM! The Great Chain of Being, Castes. All that. People were programed to think they were born into a position and HAD to listen to those above them for the most part. Education was not common, what was there reinforced the Great Chain of Being. You know what getting excommunicated in pre-1400's Europe meant? It was a death sentence. The Great Chain of Being was a part of the Catholic doctrine, and thus to deny the great chain (aka: protesting your better's actions in any way shape or form) was heresy.
Feudalism was not a symptom of indoctrination and totalitarian control; on the contrary, it's the result of the inability to exert control over long distances. The king can't move his pitiful army over from Paris to Bordeaux quickly, so he gets his nephew or one of his drinking buddies or someone he owes a big favour (at least anyone who could muster troops) to represent his interests over there. All he has to guarantee their obedience is personal loyalty, formalized in an oath. After a few generations that personal loyalty is absent (exchanging pupils/hostages was an attempt to counteract that). If one of his barons then refused to send what they perceived as their income to the king, the king had to go trounce them. Of course, if he did that everyone else would refuse to pay taxes as well, since he only had one army. So instead, a lot of envoys were sent back and forth until an agreement was reached. That could simply mean tax reduction, or anything else could be drawn in as well.
2)Actually only in DF, period wise it was still not a valid method because most places were built to be self sufficent. Do you know how HARD it was to maintain communications and other things after the fall of the roman empire? Once their roads broke down? Trade in europe almost came to a stand still until the Bergs began to form (proto-cities). I'm not saying it wasn't happening, but the general concensus was that either A) my vassals give me the stuff I need from taxes and may request a tiny bit from me if they need it, or B) I can go raid my next door neighbors at lance and sword point and FORCE them to give me what I want, or C) I can do without.
If we're talking a full blown siege or blockade? Again, not common until the age of sea except for land based sieges. And those are basically what we go through now. NO GIANT CATAPULTS! NO TREBUCHETS! Just a bunch of guys camped outside taking any supplies meant for the City/Castle/Keep until somebody starts waving the white flag.
I expect to see the whole range of economical development from (barely) self-sufficient freshly founded villages and nomadic tribes to prosperous trade centers where almost half of the population is not involved in food production. Tolls wouldn't be worth much without much trade, but that only makes the local mill rights, mortmain etc. more valuable. The raiding only happens when the nominal king or emperor
can't keep his vassals in line - let alone demand more than symbolic taxes.
4)Yeah. Missionaries were about it. And that only worked on Heathen lands, and didn't stop the Crusaders from coming in and still lopping off christian heads. Sorry, the crusades ended more christian than Muslim lives by the end of them (and that is NOT including the crusader casualty list, nor those who the Muslim's killed. That's taking the kill list of the Crusaders ALONE).
There were plenty of conflicts of interest and viewpoint even within Christianity. Every religious order is a different viewpoint (franciscans, cistercians,...). Even before the Reformation there were plenty of heresies and doctrinal disputes with political links (arians, nestorians,...) and then we still didn't mention orthodox vs. catholic.. A lot of manoeuvering behind the screens happened to determine which faction got that new church over there, or who could convince lord Longshanks to donate that piece of land to their monastery and not that other heretic order.