1. Paul versus Virginia
The U.S. Supreme Court Case that established that insurance was not interstate commerce, could not be federally regulated, but rather could only be regulated by the states was "Paul versus Virginia".
A U.S. Supreme Court decision in 1869, Paul v. Virginia, stated that insurance is not interstate commerce subject to the Commerce Clause in the U.S. Constitution.
As a result, the regulation of insurance was left to the states until 1944.