Zechariah 12 describes a "great mourning in Jerusalem" where the families of the land mourn "apart." John takes this specific imagery and applies it to the imminent coming of Christ in Revelation 1:7: "Behold, he is coming with the clouds... and all the tribes of the earth [land] will mourn over him."
This was not a global mourning of every individual on the planet, but a localized, covenantal mourning of the tribes of Israel. When Christ "came" in judgment using the Roman armies in AD 70, the apostate nation realized—too late—that the One they had pierced was their King. Their mourning was the bitter realization of their own self-destruction.