Before 212, for the most part only inhabitants of Italy held full Roman citizenship.
Emperor Caracalla declared that all free men in the Roman Empire were to be given theoretical Roman citizenship and that all free women in the Empire were to be given the same rights as Roman women.
How did the inhabitants of Italy react, giving that they had lost their privileges over the colonists?
I want to point out that many people outside of Italy were Roman citizens by 212. I couldn't really tell you how they reacted to the Constitutio Antoniniana, but I could give you an idea of some of the wider and long-lasting effects of the decree if you're interested?