To me the funny thing is that the scriptures they use about that (preaching to all nations) as well as the "end of THIS system of things" always has to have a connection with OUR DAY. HELLO! Some scriptures may be fulfilled more than once because things (Like the ENDING OF SYSTEMS OF THINGS...i.e. "way of life", "governments" etc) happen over and over throughout history. Jesus and the Apostles were living in the era of the ROMAN EMPIRE...the end of Jerusalem's system (temple, way of life) was about to end. Nations rose against nation in those days too. How did Babylonians ever gain power? There were wars to be fought. Even God's chosen people fought in battles.
But see, the Witness really mean that THEIR Good News will be preached...when in fact, the Good News that Christ brought is known all over the world. More people know of the Gospel (of Jesus) Globally, than they do about a religious Cult called WTBTS or Jehovah's Witnesses...even tho the Watchtower is the most published magazine in the world. (funny how they always BOAST this at meetings)