There is tribulation & there is Great tribulation. Great tribulation begins the moment the man of sin stands in the Holy Place and shows himself to be God. This must take place before Jesus will return. Jesus is the one that gives the deadly wound to the beasts head the dragon gave his power, his seat, and great authority to in Revelation 13:2. After that he sends the angels of God to Gather the 144,000 from the twelve tribes of Israel. After these are sealed, the multitudes are taken out of Great tribulation to the throne of God. i.e. the Rapture.