Final answer:
In response to the Christiana incident in 1851, the federal government sent marines and attempted to prosecute those involved for treason. However, local juries refused to convict, reflecting the North's growing resistance to the Fugitive Slave Act of 1850, which was seen as an imposition of pro-slavery federal power over state and individual rights.
Step-by-step explanation:
The incident at Christiana, Pennsylvania, in 1851, where a slaveholder was killed while trying to capture his escaped slaves, led to a significant federal reaction. Under President Millard Fillmore, who was pressured by southern interests to enforce the Fugitive Slave Act, the federal government responded by sending marines to apprehend the runaways and those involved in the slaveholder's death. The efforts to prosecute the resisters for treason, however, failed to yield convictions, as local juries were unwilling to convict them. This defiance was a source of horror for southern slaveholders, who expected the federal government to protect their property rights, even if it meant imposing on northern rights to free speech and local autonomy.
The Fugitive Slave Act of 1850 was a particularly contentious piece of legislation because it expanded federal power and required northerners to participate in the capture of escaped slaves, and it discouraged the use of local and state authority to counteract its enforcement. This law deeply troubled northerners who saw the corrupt nature of the rulings, where commissioners were financially incentivized to rule in favor of slaveholders. Consequently, northern resistance increased, with public opinion in the North turning even more strongly against federal enforcement of pro-slavery laws.