"The Federal Bureau of Investigation had virtually no intelligence on the Mafia families, the largest crime syndicates in the United States, through the late 1950s." Mob and the City, p. 220.
This is a misleading statement. If you read Virgil Peterson's testimony at Kefauver in 1950, he and other agents definitely knew what was going on at some level. At the Federal level, the FBN had tons of intelligence and were feeding that information to the senators on the Kefauver panel. The FBN and FBI probably weren't sharing information. As far as national security, Hoover set top priorities elsewhere like the growing threat of Marxist Communism and Nazi spies during WWII etc. People who lean far to the left minimize or ridicule the Communist threat.
As far as Appalachin, it forced Hoover to change his focus, but there were plenty of people in law enforcement who knew exactly what was going on years before. The notion that no one knew anything prior to Appalachin is a big lie.
