On January 31, 1969, the Confederation Bureau of Investigation revealed the existence of a major Mexican spy ring in Michigan City targeting the North American atomic weapons research project there. The revelation caused the two nations to sever diplomatic relations with each other. Raphael Dominguez, the nominal President of Mexico, released a statement that said, in part, "We are surrounded by enemies, and a cornered nation, like a cornered man, must often strike out in self-defense. This is not a threat, merely an observation. I hope our enemies understand the meaning of my words and will act accordingly."
Dominguez's remarks appeared the next day in the Mexico City Times.