Isn’t it logical that in order to destroy this nation, the fastest and easiest way would be to keep its national borders unchecked? Nothing magical about it.
It was, and is, a purposely executed take-down measure.
Step 1 was to debase the republic by granting practically universal suffrage - including members of the dependent looter class.
Step 2 was to greatly expand the new voting class created in step #1 by all means fair & foul.
Democracies are an automatic fail - no ands, ifs or buts. So, the absolutely sure fire way to destroy a country is to enact democratic rule. Once that is achieved, history is on auto-pilot.