When you see these things happening, know that the Kingdom of God is near. After the somewhat ‘graphic’ description of the end times, and knowing that his listeners might have gotten scared, Jesus moves to calm them down by saying all that he had described would culminate in the appearance of the Kingdom of God (to be understood as the salvation of believers). In other words, even though some terrible things would take place, things that would lead many to question their faith in God and in the endurance of the good over evil, the ultimate victor will be the good. Evil will never triumph over good, and the apparent reign of evil will always be short-lived. 
The Kingdom of God is always understood as synonymous to the Messiah and his ministry (mission). It is the coming of the Messiah that inaugurates the Kingdom. Jesus had already identified the beginning of his public ministry with the in-breaking of the Kingdom (cf. Mark 1:15; Matthew 12:28; Luke 10:9, 11:20, 17:20-21). The ministry of Jesus had already inaugurated the Kingdom of God since the kingdom is all about restoring the triumph of the good over evil. Thus, when Jesus talks about the catastrophic events of the end times signaling the nearness of the kingdom, he is pointing to the apparent reign of evil coming to an end. Evil will be overcome by good for ever.