The World Is Mourning

Revelation 1:7

This mourning could speak of a rejection of Jesus, i.e. mourning that Jesus has come to take over their nations. Or it could mean a process of repentance due to Jesus’ death, i.e. a realization that Jesus died for them and so weeping over their own sin.

Probably the first, since that seems to be the context of Daniel, Matthew and Mark. And, honestly, the only mourning that takes place in the world in the book of Revelation is that of sorrow that their world is taken away from them.