I think there is some misunderstanding here! The open borders of Eastern Europe were opened by the Communists, not the West. The Communists had, up until the end, kept everyone effectively in prison by closing the borders. Just prior to the fall of the Berlin wall, massive migrations from the Czechs were allowed and it became very clear that lots of people would leave if they could. This was a relaxation of the closed borders by the Communists. They actually had automated machine guns on some fences to keep people IN.
Please do not confuse this with the "open borders" and "free trade" problem we face with Mexico. It is totally different.
Closed borders is what Kim wants, not us.
Kim is trying to get us to pay extortion money for him not to pursue the acquisition of nuclear weapons and delivery systems.
We should not pay. The Clinton administration agreed to such an arrangement in the 1990's and it only resulted in resources for Kim's regime and time.
And, correct me if I am wrong, wasn't the actual fall of the Wall in E. Germany precipitated by a miscommunication between Moscow and the E. German leaders? The E. Germans thought they were following orders and once they realized what was happening, it was too late; the floodgates had been opened.