Fugitive slave laws were very controversial because they allowed
slaveholders in the South to?

The fugitive slave act allowed slave owners to have their slaves returned to them even if they were in a free state or country.

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the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.