How does Harriet Jacob's narrative help us understand why war broke out when it did?

The primary goal of Jacob's narrative, as with many slave narratives, was to appeal to liberal whites. Although most Southern rural whites were in favour of the slave-trade there was a growing abolitionist movement including Quakers who were sympathetic to the slaves' plight. Certainly narratives like this spread the cause to educated (one's who could read) and progressive whites.