What is the basis for arguing that the gospel has already been preached to "all nations"? In Matthew 24:14 (cf. Mark 13:10), Jesus says:


  And this gospel of the kingdom will be proclaimed throughout the whole world as a testimony to all nations, and then the end will come.


Many Christians understand this to be a sign of the end times: that Christ's Second Coming will only occur after every "nation" (or people group) on earth has heard the gospel. There are many unreached peoples around the world, the argument often goes, so Jesus won't return until this missions work is accomplished.

Is this the only way to understand this verse?  Specifically, if this verse is a true prophecy of Jesus, what biblical arguments are used to show that it has already been fulfilled?
Some argue that "throughout the whole world" here is best interpreted as an 


  indication of the universal offer of the gospel to all nations, i.e. outside the confines of the Jewish community.


This is possible since the literal meaning of the word for "world" here is "the inhabited area," and often indicated simply the Roman Empire or the known world.1,2

Two verses in particular are often used as evidence of this alternative interpretation. Colossians 1:5–6 reads:


  Of this you have heard before in the word of the truth, the gospel, 6 which has come to you, as indeed in the whole world it is bearing fruit and increasing (ESV)


Colossians 1:23 is even more clear:


  if indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel which you heard, which was preached to every creature under heaven, of which I, Paul, became a minister. (NKJV)


Paul's language here and elsewhere (cf. Romans 1:8, Romans 10:18) is seen by some to be a confirmation of the words of Jesus, that the gospel had spread "universally" during the apostolic age. 

Preterist J. Stuart Russell also sees a parallel passage in Matthew 10:23:


  Truly, I say to you, you will not have gone through all the towns of Israel before the Son of Man comes.


This he sees as consistent with Matthew 24:14, and argues that 10:23 refers to evangelizing Israel just as 24:14 refers to evangelizing the Roman empire.  He concludes:


  The wide diffusion of the gospel, both in the land of Israel and throughout the Roman empire, is sufficient to justify the prediction of our Lord [in Matthew 24:14].3




References and notes


R. T. France, The Gospel According to Matthew
Many commentators take the passage this way, including Albert Barnes, People's New Testament, John Wesley, and Thomas Coke.  Wayne Grudem mentions this understanding as a possibility in his Systematic Theology, 1101–2.
The Parousia, 71