Final answer:
John Brown served the antislavery cause through his advocacy and participation in violent uprisings against slavery, particularly with the raid on Harpers Ferry.
Step-by-step explanation:
John Brown best served the antislavery cause by leading violent uprisings against slavery. His most notable action was the raid on Harpers Ferry in 1859, which was an attempt to initiate an armed slave revolt. Brown's actions brought national attention to the abolitionist movement and escalated tensions leading to the Civil War.
While some saw him as a martyr, his radical approach was at odds with more peaceful abolitionists like William Lloyd Garrison.