The difference between "BTN" and "BT" policies are not so stark as they were before, say pre-WW2. With an increase in the interconnectedness of markets and direct foreign investment, what one country does domestically has a huge effect on others, even if the original intention was not to raise oneself up at the expense of others (in the zero-sum scenario you mention). The case of the financial crisis in the U.S. and Greece are clear-cut examples of this. Indeed, BT policies can turn into BTN policies quickly, especially when aided by poor regulation (in the E.U.) or weak governance (in developing countries).