"Sixth Column" by Robert Heinlein
https://www.amazon.com/Sixth-Column-Robert-Heinlein/dp/1451637705/

A standalone science fiction book, no prequel or sequel that I know of.
I read the well printed and well bound trade paperback published by Baen
in 2012 that I bought new on Amazon. The book was written in 1940 by
Robert Heinlein and first serialized in Astounding Science Fiction in
1941. The book was first published in hard back in 1947 by Gnome Press.
The book was published in paperback by Signet in 1949 as "The Day
After Tomorrow". Heinlein habitually sold his stories to a magazine, a
hardback publisher, and a paperback publisher to maximize his revenue
for the first twenty years of his career and advised his writer friends
to do the same.

Heinlein actually wrote the book as a project from John Campbell who
provided a detailed outline for him. Campbell had already written a
novella about the story which, he did not foreclose to Heinlein, but his
employers forbade him to publish it, especially at a competing
publisher. It was Heinlein's second published book.
https://en.wikipedia.org/wiki/Robert_A._Heinlein_bibliography

This is a controversial book. It has the USA invaded by the PanAsians,
a conglomeration of Japanese, Chinese, and Russians, taking out the main
population centers of the USA using nuclear weapons and then landing
troops, lots of troops. The year of the invasion is not identified but
it could have been anywhere from 1942 to 2050. Plus the book has a
large amount of handwavium for the mysterious Ledbetter effect, a new
type of rays.

The book has a forward by William H. Patterson, Jr. and a afterword by
Tom Kratman. William H. Patterson, Jr. wrote a very large two volume
biography of Robert Heinlein. Tom Kratman addressed the times that the
book was written in, at the very beginning of the time that the USA
joined WW II, already in progress in Europe and in the Pacific. People
already knew that there was a lot of crazy going on in the world
already. By the beginning of 1941, the Germans had already defeated or
occupied Austria, Poland, France, Netherlands, etc, the Japanese had
defeated China, Korea, etc, and the citizens of the USA well knew it.

My rating: 4 out of 5 stars
Amazon rating: 4.4 out of 5 stars (489 reviews)

Lynn