Paul considered the gospel fully preached in "all the world" :
(Mark 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.)
(Col 1:23 If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister)
Paul is using Jesus' own words "every creature".
Paul's ministry was to the world "his course":
(Acts 20:24 But none of these things move me, neither count I my life dear unto myself, so that I might finish my course with joy, and the ministry, which I have received of the Lord Jesus, to testify the gospel of the grace of God.)
He here he states he's finished his course:
(2 Tim 4:7 I have fought a good fight, I have finished my course, I have kept the faith)
(Acts 2:5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.)
As for the context of "all the world" it should be understood as a "Jewism" with some hyperbole thrown in:
(John 12:19 The Pharisees therefore said among themselves, Perceive ye how ye prevail nothing? behold, the world is gone after him.)
Babylon is apostate Israel which killed the prophets the prophets and apostles are told to rejoice over "her"
(Rev 18:20 Rejoice over her, thou heaven, and ye holy apostles and prophets; for God hath avenged you on her.)
(Rev 18:24 And in her was found the blood of prophets, and of saints, and of all that were slain upon the earth.)
There is only on entity that was guilty of the blood of the prophets - Jerusalem:
(Luke 13:34 O Jerusalem, Jerusalem, which killest the prophets, and stonest them that are sent unto thee; how often would I have gathered thy children together, as a hen doth gather her brood under her wings, and ye would not!)