Financing the Civil War

 The American Civil War cost the federal government more than $3 billion, and much of the money was raised from the sale of Union bonds. As well as relying on ordinary Americans to finance the war, a lot of investment came from overseas, as US securities became a global commodity during that era.

...

By the Reconstruction period a new financial order was emerging. In October 1868, Hunt’s Merchant Magazine proclaimed that $700 million in US securities was foreign owned. A year later, this number had climbed to $1 billion and nearly half of US debt was owned abroad. The spread of such sales abroad reveals, among other things, the emergence of the German economy centered in Frankfurt.

http://community.bowdoin.edu/news/2017/01/bonds-of-war-david-thomson-08-on-financing-the-civil-war/#:~:text=The%20American%20Civil%20War%20cost,global%20commodity%20during%20that%20era.