They have their own tunnels.
Of course, I doubt anyone can guarantee 100% security, but to say security is a useless exercise for that reason is nonsense.
I would say that restricting trade and travel is against Natural Law.
Would be your prerogative.
The facts speak for themselves.
Correlations for most anything can be found if you look for them, does not establish fact(s).
It isn't correlations they are talking about, it is predictive power. Restricted trade leads to war, while vigorous trade prevents it.
All reliant on their correlations of past history. Hell, one could show causation(s) from anything if so inclined. Of course integrated trade would be a factor, and less of incentive, that's a no-brainer. But to state it's a barrier is misleading. Is/was trade relevant to ISIS, was it to Hitler, Castro, Stalin, Mao, Ho Chi Minh, et al. In some cases trade may have became a later issue , but not the reason(s) for the initial aggression(s). Ownership, plain and simple would most obvious be the greater incentive, not trade imbalance.
Yes, trade was extremely important to those people, and economic issues are what most people attribute the rise of Nazism and the fall of Communism to.