You can't really aggregate trade at the country level. Well, people do that all the time, but you can't expect it to follow the same rules as the real market.

People participating on the international trade are better off. There are plenty of cases of market failures (monopolies, etc), inertial problems (deflation, etc), or human capital destruction (due to worsened wealth distribution) predicted by theory already. Any of those can overwhelm the usual net positive contributions of trade.