Empirical evidence of the impact of borders on international trade flows using the gravity equation approach abounds. This paper examines the empirical relevance of state borders in U.S. interstate trade for various specifications of the gravity equation. We find a large and economically...

In this paper we examine the empirical relevance of three prominent endogenous protection models. Is protection for sale, or do altruistic policy makers worry about political support? We find strong evidence that protection is indeed "for sale". The important new result is, however, that not...