Two important points about the Second Fugitive Slave Law are the reactions of the Northern whites and the reactions of Northern blacks. Your topic sentences might reflect these reactions.
Possible ideas for topic sentences:
Northern whites were angry that the Law forced them to assist Federal Marshals in the capture and return of alleged run-away slaves.
Northern blacks were alarmed by the Law and many escaped to Canada, whether they were peacefully settled escaped slaves of blacks born into Northern freedom.
The Second Fugitive Slave Law inspired the growth of Abolistionist Movement flamed by Northern outrage and sense of justice in the face of the Laws injustice.
Another point to add might be the uneven payment scale of $5 to $10 for hearings that dismissed a finding of a run-away slave versus those that found for an owner reclaiming a run-away slave.
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