The Church doesn't recognize marriages that did not take place in the church, so they essentially never happened.
The Church presumes all Christian marriages to be valid until shown otherwise; the divorce culture has made this presumption increasingly shaky, but it still holds.
That depends who the parties are. Marriages outside of the Church between parties who are not Catholic are recognized as valid by the Church. For a Catholic to marry outside of the Church either a dispensation for disparity of cult; Catholic and non-Christian, or permission for a mixed marriage; Catholic and non-Catholic Christian, is needed.