The real solution is to force these kingdoms to build permanently open gates and roadways that connect the land, increase all around traffic and opportunity.
Only when people turn from digital vassals to digital citizens will we emerge from the middle ages we are currently in. In this sense the most important development in the online world is still ahead if us.
It goes to show that every generation has to internalize the painful way key facts about what is good and what is bad for society, even if history provides more than enough learnings for free.
NB This was ~45 years ago - I doubt such things would be tolerated these days. :-)
Mind you, the fact that it was events on the Isthmus of Panama that were one of the main causes of the union is fairly interesting: