I have no idea the exact year I read this short story, but I would imagine it was the 1980s when I did. It was probably part of an anthology, which usually was mid-twentieth century. I remember reading a lot of scifi from the 1940s and 1950s. The story had an old flavor to it, so I doubt it could have been much after 1965, but that is just a guess. So I would guesstimate 1945-1965?
In it aliens were about to invade Earth, but as Earth was united and peaceful it had no opposing force. All I remember is that some agents went on the Eiffel Tower and spoke in front of others that it was a shame the Eiffel Tower would be destroyed soon.
The others who overheard this reported it and an arms race began so they were ready by time aliens arrived.