Strange as it seems to us now, during the early phases of the "Unipolar Moment" and enduring for at least the entirety of the 1990s, there actually was some very strong indications to suggest Mexico could plausibly be added to the United States. Noel Maurer, of SHWI fame, had this to say some years ago: Noel worked for the U.S. Federal Government for about two years in Mexico and is an Associate Professor at GWU, so he does have some credentials to be speaking on this. As for the Este País poll, here is a citation of it. Just shy of a decade later they asked the same question again and found the support had endured. Outside of the 59% supporting it on the pre-condition of improved living standards, 21% supported doing such without any pre-conditions. So, what could be the catalyst for such occurring? @Roberto El Rey excellent Second Mexican Revolution offers a potential PoD. Way back in 2006, @Blockhead had his own War of Mexican Intervention timeline that postulated the Chiapas Crisis resulting in this.