What was dred Scott biggest accomplishment?

Answer 1

In a roundabout way, you could say he contributed to the abolition of slavery, though he inadvertently killed 600,000 young Americans before it could happen.

If Scott was wanting his freedom, he could have applied for it while he was living on free soil. By applying for it too late, when he was back in slave country, he provoked this long-running legal case that raised the temperature of the whole slavery debate, and helped to push the country into war.