Question

does anyone know why we needed a national bank
(Alexander hamilton)

Answer 1

Because our new nation was in debt after the war against Britain and we needed a national banking system to pay for the amount of money borrowed that was incurred.

Furthermore,we didn't really have a strong currency yet, and he needed an efficient way to raise money, so by forming a national bank, he could issue a national currency, collect taxes, and generally empower the country for the better...

Answer 2

A good and succinct explanation of monetary issues of the Revolutionary War and Early US is on the US Treasure website: http://www.treasury.gov/about/history/Pages/edu_history_brochure.aspx#h1

Also, I think there are references to the need for a national bank in the Federalist Papers if you want primary sources.

Good luck!
Sumana