The New-York Ledger paid Longfellow $3,000 for a single poem in 1874 (source). That was a ton of money back then, roughly equivalent to 50,000 dollars today!
Longfellow knew seven (!) different languages, and was a professor of French, Spanish, and Italian (source).
Longfellow was hugely popular and famous in his lifetime, in America and around the world. At the end of the Civil War, there were 24 companies in London publishing his work (source).
Longfellow is the only American to be honored in the Poets' Corner of Westminster Abbey, the church in London where the kings and queens of England are crowned and buried (source).