A serious factor contributing to the unrest is the extreme age and failing health of the much-beloved king, who has held the country together in the past. Technically a constitutional monarch, King Bhumibol has been much more active in national affairs than modern European royalty. It would appear that his deteriorating health no longer permits this involvement.
Until quite recently, I would have said that political upheavals in Thailand are essentially nonviolent. Most have been, this one certainly is not.
The rebels are called "red shirts" but nobody seems to say they are Communists. I suppose this is because most Thais are quite serious Buddhists.