In the US it's seems much harder, Catalonia is very small but a (semi) independent entity under the 'law' of Spain (kinda like the Dutch were). On foot some one can reach in one or two days any destination in Catalonia so it's easier to protest anything.

Hmm why it's all happening together is kinda like the 'suicide virus' once it's in the air and the message is 'we are not content' it can easily spread, everyone got something they are not content with. Like there are also a lot of small protests going around from since I was born, with the internet they all combine. A lot of twitter/facebook-ish clones are made by protestor groups and because everyone knows facebook the whole online revolution is a thing the public can handle.

A lot of disinfo is going around from both parties (although, not in Catalonia, that's just plain oppression and a political trail). It's very cyberpunk like, it's one big riot and every party that you can clearly label is wrong (again, Catalonia being an exception). The hooligan culture (from soccer) plays a big part too in Europe, they are banned from games, so they throw rocks at other events where there is police.

When the 'sport'-fans in the US join the protests it's going to be mayhem.

A song for the real revolution: https://www.youtube.com/watch?v=zm071U5p3Xw