Removal of state-court-filed litigation to the federal courts (a concept unknown at common law) is not expressly provided for in the Constitution. Martin v. Hunter’s Lessee, 1 Wheat. (14 U.S.) 304, 349 (1816). Nonetheless a limited right of removal was included in the initial Judiciary Act of 1789 and, with periodic modifications, it has remained an integral part of federal jurisprudence ever since. Those modifications duriin the doctrine’s first century culminated in a major statutory alteration...