While the California Three Strikes law imprisoned thousands of people due to its harsh provisions, the effect of three strikes laws in most other states was muted or non-existent. By 1996, the federal system had less than ten three strikes conviction, as did twelve of the states with such provisions.
From a 1998 RAND Report:
Not surprisingly, as a result of these smaller triggering-offense lists and incremental changes, much smaller numbers of offenders have been sentenced under these laws. For example, by the end of 1996, Washington had admitted only 85 offenders to prison under its law, which went into effect a year earlier than California’s (Clark, Austin, and Henry, 19971.0 By September of that year, six states which had implemented three strikes in 1994 or 1995 had not sentenced any offenders under the law.* Twelve other states and the federal system each had ten or fewer three-strikes convictions (Campaign for an Effective Crime Policy, 1996). (Link)
Black Silent Majority notes that black communities were active in 1970s tough on crime campaigns.
California Three Strikes goes into details on the California law, which was harsh.
The federal three strikes law had little impact on incarceration rates, at least at first. See True Impact of Federal Three Strikes
Washington State Three Strikes started the whole thing, but applied to very few criminals.