Dear tsuwm: I did find a quote, but I wonder how many Americans ever heard the word used?
TRIUMPHALIST 90'S
PRELUDE TO 21ST CENTURY



By Paul Kurtz

If the 1890s were called the Gay '90s, the 1990s should be heralded as the Triumphalist Decade. For at the end of the 20th century, America
reigns supreme - not only as the major military-industrial power in the world, but also as the leading infomedia society. Its undisputed scientific
and technological superiority have made it the unchallenged leader of the new global economy.

I also found this in an official Catholic site:
Protestants, who have no wish to subject themselves to Catholic discipline, often resent Catholic teaching authority. Some have
coined the word "triumphalist," from the Latin triumphus, public rejoicing for a victory, charging in effect that the Catholic Church
thinks it is better than the Protestant churches.

But I still don't know what the original quoted sentence means. For a book about English, I think
it stinks.