So I have now seen Episode III twice and still have some puzzling questions about events that happen prior to a New Hope. George Lucas answers some obvious questions...such as how Leia and Luke get seperated, how Yoda ends up on Degobah...etc.. but where does the Rebellion come from? Im guessing that it arises because of the Emperors Supreme control, but Lucas doesn't really give us a good answer. A good explanation would be helpful.

 

By the way did anyone else dislike General Greivous in the movie?....He was a little fake for me to take seriously.

All over the place, sort of. To the best of my knowledge it began as a group of disgruntled ex-senators from the Old Republic and attracted all manner of miscreants and malcontents. When the Empire began throwing its weight around, whole systems (mostly ones on the rim) started covertly supporting the rebels, and after they'd won a few major battles those systems began openly declaring their revolt. By the end of ROTJ I guess the Empire had little in the way of popular support from anyone, since it'd already dissolved the senate (?).

 

I thought Grievous was lame and pointless as well, apparently you had to see the Clone Wars cartoons to really get the reference.

The flags you see at the end of ANH are the flags of those systems who have joined the rebellion at that stage.

http://www.starwars.com/databank/organization/rebelalliance/?id=eu

I recall reading in one of Zahn's books how it was mentioned that the rebels were fortunate they had never encountered the full might of the Empire. Supposedly the Empire's vast fleet was in fact having to patrol and maintain order. Something that the New Republic would not realize until they had dissolved to the point of nothing militarily and planets and other systems started feuding with one another.