There was a time when it was considered necessary and proper to be concerned about possible foreign influences in US government and military service. Way back in 1981 when I first filled out forms as part of the process for joining the US military (it was a DOD form, I don't remember the number) I had to answer a specific question regarding travel. The question asked if I had traveled to any of a list of nations after certain dates (all communist bloc countries) with a date listed by each nation (the date that each country had turned communist).
Anyone who joined the military in the Cold War era probably remembers this form and this question. If the answer to the question for any of the nations involved was "yes" you had to provide a complete explanation for the reason for the trip, when it took place, etc. Having never visited countries like Cuba, North Korea, East Germany, the Soviet Union, etc., I can't say that I know what the process would have been had I answered yes.
But the point is, if you wanted to join the US military and you had even visited any communist countries, the Department of Defense wanted to know about it.