Please help me rephrase the following sentence. It is from a novel set in the last decades of the 19th century, in Ottoman empire.
"We have some family in New York, but they are so well integrated that they look down on those of us who settled in Istanbul. We are too backward for them, but not for
the letters of credit from the firm of my maternal uncle (who was a trader). Our wealth, however, is perfectly acceptable."
I found the definition for the letter of credit, but it is a modern term which, i believe, didn't exist in 19th century. Could it be some kind of loan? Or a guarantee? Or is it he just sent them money?
Thanks!
Lucrezia