There's nothing, including the US, forcing North Korea to do what they are doing. Which, sort of, is the idea in the first place.
No one is ever forced to do anything, philosophically.
Imagine, though, that half of Cuba, had been occupied by US forces following the bay of pigs, which had then created West Cuba. Do you think it unlikely that this would have made Communist Cuba more intolerant of opposition and more militarist? With that the case, would such a development have a) increased the possibility or b) decreased the possibility of Cuba coming under the control of its military industrial complex?
Or, imagine that North Vietnam would never have triumphed, but Vietnam would have remained divided. Do you think such a country would have been as likely to open up in the middle of the 80s? Or would it have increased the possibility of Vietnam being ruled by die-hards hoarding weapons for a eventual second go at unification and mercilessly prosecuting all internal dissent? And, if South-Vietnam turned out to be an economic success, do you think that the North-Vietnamese die-hards would be more or less willing to reform then the government of, say, Laos, considering that such a reform would dramatically increase the risk of collapse and absorption into South-Vietnam, depriving the die-hards of their position and their ideological justification?
So no, history is not made by evil men. I'm sorry, but its much more compelx then that.