Why did the raid on Harpers Ferry fail?

Answer 1

The capture of the Federal arsenal at Harper's Ferry was a short lived success. John Brown succeeded and from that point he and his followers tried to instill a slave rebellion in Virginia. The attempt to encourage slaves to revolt had no support from slaves or anyone associated with Brown's attempt. Ultimately, the US Army recaptured the arsenal and captured Brown. The cause of the failure was Brown's ill conceived idea that slaves would rush to revolt.

Answer 2

because brown used violence and lost most of his untrained soldiers and they ran out of supplies like food