Yeah you didn't just take Moravia. For a coalition that large and distant to form, you must have committed a number of aggressive actions such as fabricating claims and getting caught (that alone can cause coalitions to form), annexed multiple provinces, force vassalised someone, or any combination of the aforementioned. One province alone won't generate a coalition like that.
Take a look at your AE in the diplo screen of one of your neighbours. That will be why.
Take a look at your AE in the diplo screen of one of your neighbours. That will be why.