The supposed benefit would have been the return of lost territories during the Mexican-American War (1846-1848). Specifically, Texas, New Mexico and Arizona. It however was unfeasible because Mexico was in the middle of its Mexican Revolution (1910-1921).
Japan was in the allies. Japan joined the allies because Germany had a part of china and a few islands in the pacific and Japan wanted to conquer the german land.
Zimmerman telegram
Zimmerman
Verbundeter
Cuba was an ally to the US during World War II. But after the war, Cuba became communist and joined on the side of Russia against US. Cuba and Russia were also launched the nuclear threat on the US and Mexico.
It was believed that if Mexico could fight the United States that the United States would not enter the war on Germany.
Hitler.
they got in a huge fight Spain an German so some ally of German wanted to learn Spain patriots
Italy was the country that, under Benito Mussolini, was an ally of Germany, until the Italian people deposed the dictator, and Italy became an ally of the allied powers.
The Underground Resistance Network would have lost the perfect place for spiriting people out of France and other nations. Many downed airman and Jews were able to use Spain as a place to escape to and to leave from for safer horizons. If Spain had joined Germany the Allies would have had to fight them and invade their nation too. It would have been much harder for the Allies to defeat Germany if Spain had joined Germany in the war.
Germany was attempting to get Mexico as an ally. The US was headed for Europe in '17; didn't need to have to fight Mexico so close to home.
America never joined/allied with Germany in World War I and II. America was an ally and Germany was an axis. But America did join partially because of Germany. Germany announced that they would use their submarines on anyone and America felt threatened and decided they needed to take action. Germany also contacted Mexico and asked Mexico to help Germany defeat America.