Indeed, it could be argued, from a certain perspective, that the 1990's drop in murder rates was actually a result of more draconian measures being adopted, at both a state and federal level, to tackle crime, as well as, potentially, efforts to implement laws reducing gun crime, such as the Brady law.
No correlation between gun control and violent crime or murder in the US. National Firearms Act 1934 preceded an steep decline, but Gun Control 1968 preceded an era of record violent crime and homicide.
The difference is our resolve to tackle organized crime. Three-strikes, RICO, and mandatory-minimums have created a record number of inmates, some of whom never even committed a violent crime, but it has been effective for keeping organized criminals locked away. FBI publishes crime reports periodically. They associate about 50% of our homicides and violent crimes to gang activity and organized narcotics trade.
Abortion is an interesting theory, but it will eventually have no correlation as abortion rates fall in the US and birth control becomes more prevalent.
