What did the author mean when he said, "the cause of america" is "the cause of all mankind"?

When the author said "the cause of America" is "the cause of all mankind, he is referring to the worldwide plight of people under oppressive government and all of those individuals are struggling against them, the struggle for the cause of America is a symbolic statement for the struggle for the cause of humanity worldwide wherever the same kind of circumstances are found.

an era of negotiation.

is that an answer to your question?