Many say that many of the events prophesied in the Olivet Discourse have not yet taken place and must future. One reason is they say the Gospel hasn't been preached in all the world as Jesus predicted. But the Apostle Paul, under inspiration of the Holy Spirit said otherwise.
And this gospel of the kingdom will be preached in all the world as a witness to all the nations, and then the end will come.
3 We give thanks to the God and Father of our Lord Jesus Christ, praying always for you, 4 since we heard of your faith in Christ Jesus and of your love for all the saints; 5 because of the hope which is laid up for you in heaven, of which you heard before in the word of the truth of the gospel, 6 which has come to you, as it has also in all the world, and is bringing forth fruit, as it is also among you since the day you heard and knew the grace of God in truth
21 And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled 22 in the body of His flesh through death, to present you holy, and blameless, and above reproach in His sight— 23 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.