It seems easy enough to claim Jesus was speaking about a first century generation, however, logic ends there when one contemplates the fulfillment of all Bible prophecy. In order to make 70 AD the magic year, you would have to delete dozens of prophecies that were never fulfilled. The questions are endless. Preterism produces some very bizarre explanations for why the world is still experiencing suffering and calamity. One explanation I ran across cited God's need for population control as the reason for mankind's suffering.
Kingdoms rise and kingdoms fall.
God is the providential population controller. He brings famine, disease, natural catastrophes, wars and tumults. 850,000 were killed in the 1556 earthquake in the Shanghai province of China. 13 million were killed under Stalin and 6 million under Hitler. God is very equipped to control population.