Answer:
It dramatised the whole issue, by bringing the effects to their front door, in the form of official slave-catchers newly employed to hunt down runaways.
'Uncle Tom's Cabin' was written quickly and angrily in response to the Act.
Many Northerners who had not held strong opinions about slavery were enthused by the Underground Railroad, the safe-house system that sumggled slaves to freedom in Canada.
It had the opposite effect from the one intended - it had been meant as a concession to the South. In fact, it galvanised opinion and action against it.