Tyrants may appear to be tough, but on the inside, they're spoiled babies and weak at that. Kim Jong Un is a classic example. Weapons make him feel important. Like a spoiled child (that he still is, for he has never developed properly on an emotional level), he wants people to notice him. He craves attention, and like the spoiled child, uses negative means to try and command that attention. The problem with tyrants, though, is that they view the whole world as expendable; they readily dispose of anyone who doesn't pamper them or cater to their wims.
Kim Jong Un's people in North Korea are borderline starving. Food and power shortages are rampant, and with economic sanctions and no foreign investors (except for the terrorist countries that have been buying nuclear know-how), North Korea has tremendous economic headaches. But Kim Jong would rather have more nukes in his arsenal than a decently nourished population. So why don't they revolt? They would, but they're both scared and conditioned from years of total oppression.
Kim Jong won't make teshuva. He faces a fate similar to that of Sadaam Hussein and Bin Ladin. Tyrants don't last - they make a big splash, but always suffer a tragic end. Achmedinejad in Iran is walking down the same road, also "looking forward" to his tyrant's due.
So why does Hashem give us the Kim Jongs of the world?
Hashem wants us to make teshuva and to come back to Him with all our hearts. As soon as we do, the Kim Jongs will simply disappear - it's that simple, wait and see.