Abortion became legal in 1973. But it didn't become a common thing for a few years. The worst period for crime in the US (overall violent crime), was the mid 80s to the late 90s. By then abortion had become more commonplace and there were fewer black children born to single mothers in low income areas known for high crime rates. The decline in the number of young black men in proportion to the population of the country on the whole was significant. Fewer black males meant less crime and much less violent crime. The statistics for inner city areas didn't catch up with the rest of the country for years, and some areas are still terrible (places like Camden, NJ, St. Louis, MO, Detroit, MI, Memphis, TN, Oakland, CA, etc.), because there are lots of blacks there. Some people look for excuses, they don't like to admit that it's the truth. But it is. Blacks rob, steal, rape, assault and murder one another and other people far more than people of other races do. They're predisposed to crime.