A long time ago, if I remember correctly, Axis and Allies only had an East and West U.S. Mexico bordered both territories and then Panama bordered the south border of Mexico. The U.S. mainland was not directly connected to Panama. Therefore, U.S. forces had to first go through Mexico to get to Panama.
In AA 1942 (I don’t know about other games) the U.S. is split into three sections: West U.S., Central U.S., and East U.S. Mexico borders the West U.S and Panama borders Central U.S.
I’m not sure why they created it this way. I think that if they wanted to give Japan a chance to get a toe-hold in the Western Hemisphere they would not have had Panama connect to the U.S. Only Mexico should border both the West U.S. and Central U.S. Thus when Japan takes Panama, the East U.S. could not tank blitz it, but only the West U.S. This could buy time for Japan to move its Navy across Oceans.
Has anyone ever tried to make a serious run at the U.S. with Japan? If so, how did you do it?