1. The people depicted in the cartoon are the Nisei and Issei that reside in the USA, as well as "Japanese spies". They are apparently given "TNT" or weaponary from the Japanese government for an internal inssurection against the United States.
2. Dr. Seuss is implying that the Japanese-American would be loyal to their own home country, and would rebel against the United States, either indirectly through spying, or directly through guerilla warfare. It justified Japanese internment, as it highlights the fear of Japanese American rising up against the United States following the USA's declaration of war on Japan following the bombing of Pearl harbor.
It is worth noting, however, that many Japanese-American (Nisei in particular), had no connections between themselves and the Japanese homeland, and, when allowed to join the US military to fight in the European sector, proved to be an effective fighting force.
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