Final answer:
John Brown's notable actions prior to the Harpers Ferry raid included violent anti-slavery activities such as the Pottawatomie massacre in Kansas and raising funds for his antislavery cause, which heightened tensions leading to the Civil War.
Step-by-step explanation:
Before John Brown's raid at Harpers Ferry, he had already become an infamous figure in the fight against slavery. One of his notable pre-raid 'accomplishments' was leading an attack on proslavery forces at Pottawatomie Creek in Kansas, a violent action against slavery that marked him as militantly abolitionist. Furthermore, Brown was involved in the Free Soil movement in Kansas, where he actively participated in efforts to prevent the spread of slavery into that territory. He also mobilized financial support for his antislavery activities, notably convincing a group of abolitionists known as the 'Secret Six' to fund his planned raid on the federal arsenal. Brown's actions prior to Harpers Ferry contributed to the rising sectional tensions that would eventually erupt into the American Civil War.