Although Trade and investment among Northeast Asian countries have substantially increased since the 1990s, although there has not been any significant progress in terms of institutionalization of regional economic cooperation. On the other hand, In spite of many discussions and institutional efforts to enhance cooperation in energy development, railway construction, and the environment, few tangible results have been realized. Another key characteristic of Northeast Asian economic cooperation can be found in its international political constraints. Political tension among Northeast Asian countries, partly due to historical matters, has been exacerbated recently. (The rest is omitted.)