The real goal was to maintain control of the South's economic activities and prevent them from becoming a threat to the powerful men in the North who's ideological descendants have been controlling Washington DC ever since.
Well then I guess we'll all have to decide what to believe, you or our lying eyes.
In 1860, the Federal government's prime source of income was tariffs. Tariffs were collected on import goods. Import goods were paid for with export goods, of which the South produced 73% of the total export value for the entire nation.
They were creating the import traffic that paid the taxes into the Federal government, and since they created 73% of the export value, they effectively created 73% of the return import value, on which the tariff's were collected.
The Southern 1/5th of the US population was producing 73% of the taxes, while the Northern 4/5ths of the population was only producing 27% of the taxes.
Don't take my word for it. Look it up here.
But only look it up if you want to know the truth. If you want to continue enjoying your comfortable myth, then by all means refuse to look at anything which proves it wrong.
Oh, and by the way, that book was written and published by a New Yorker in 1860. He was a Northerner and it was before the war when it was published.