Published in Astounding Science Fiction, Feb 1945.
To stop endless wars on Earth, and to convince all humans to unite together under a common cause, Mr. Whitlow is on Mars trying to persuade the ancient Martian race of Coleopteroids, a black, oval, yard-long, double-shelled, and telepathic species, to launch a limited attack against Earth. Unfortunately for Mr. Whitlow, the Coleopteroids are unconvinced of his arguments of humanitarianism or loot. It is only after Mr. Whitlow becomes resigned to failure that he unwittingly gives the Coleopteroids a reason to take the matter seriously.
Wanted–An Enemy was written in the last year of World War II when Fritz Leiber was 35 years of age. Born in 1910, Leiber was a child during World War I, and also lived through the Great Depression. Leiber's experience of the world at this point was of two total wars and the greatest economic collapse of modern history. Certainly, it must have seemed from this perspective that humanity was out to destroy itself.