One of the questions the disciples asked was what would be the sign of the end of the world?

.............The phrase 'end of the world' in the KJV should read 'end of the age'.

....................................The world [earth] itself is not to come to an end, but after it has been cleansed of evil, it will continue into the Millennial age [the 1,000 year reign of Jesus Christ].

......................................The end of the age is found in verse 14 of Matthew 24; "the preaching of the Gospel to all nations."