Why Was Trade Among the Countries of Southeast Asia Low

Why was trade among the countries of Southeast Asia low prior to the era of economic development?

A) Many of the countries were at war with one another (for example, Thailand and Cambodia) .
B) Communist governments in Southeast Asia had a no-export policy.
C) All the countries exported similar goods and imposed tariffs against one another.
D) Most countries were self-sufficient and had little need for trade.