There are numerous examples where free trade between states has not prevented the war but rather escalated the war, examples that come to mind are World War I and the current Sino-Japanese conflict.
I believe the axiom if people don’t cross borders then army will is still correct but when trade is done under the “beneficial” eyes of the bureaucrats is not the kind of free trade that has quotas for countries and a policy of import=export, both of which is total bs.
Total freedom without any barriers is the kind of trade that makes war with other countries less likely.
I think that Sino-Japanese war will be determined by whether politicians from both sides can see past their noses and as a result both countries (and infact all countries reduce or eliminate barriers)
Just my two cents