Because the Navajo language is complex, and has only ~150,000 speakers, as well as (if i remember correctly) no real writing, it was hard for the Japanese to break the codes, as they didn't understand the language, and there was nothing to base their code-breakers on.
What they have in common is McDonalds and drive-in theaters both include drive-in and Levittown and Holiday Inns are both like houses and homes for people.
