In WWII ,as a veteran of such, the US had a pool of hardy young men and some good military leaders. Once we realized that the Germans and the Japs were actually going to kill us in any barbaric way the men and women of the age took things seriously and showed the Japs and Germans we could and would fight too. I believe this factor of character was something neither the Nazis or Japs realized. By the way I don’t recall Mexico being a big help if any for our efforts in WWII.
Maybe not a big help, but they were allies:
“Mexico declared war on the Axis Powers in support of the Allies on May 22, 1942, following losses of oil ships in the Gulf, most notably the Potrero del Llano and the Faja de Oro, to German submarine attacks. Although most American countries eventually entered the war on the Allies’ side, Mexico and Brazil were the only Latin American nations that sent troops to fight overseas during World War II.
Perhaps the most famous fighting unit in the Mexican military was the Escuadrón 201, also known as the Aztec Eagles. This group consisted of more than 300 volunteers, who trained in the United States to fight against Japan. It was the first Mexican military unit trained for overseas combat.
In the civil arena, the Bracero Program gave the opportunity for many thousands of Mexicans to work in the USA in support of the war effort. This also granted them an opportunity to gain US citizenship by enlisting in the military.”
-http://en.wikipedia.org/wiki/Military_history_of_Mexico#World_War_II