Makes sense though, the Battle School program spanned the entire world so of course they were pulling kids from various ethnicities. (Hey, Petra is white - Armenians are technically white, right?!) As for the other worlds, I think it was an established 'thing' that other planets got colonized by specific races - like Portugese on Lusitania and Chinese on Path. It really makes sense considering people would probably want to stick to specific ethnic groups to better understand each other, have less infighting and keep their own culture as intact as possible while still leaving Earth. I mean, it wouldn't do to send a bunch of people who inherently cannot get along ideologically to a new planet just to start blowing each other up again as soon as possible.
If anything, it's refreshing to see that the movie didn't get whitewashed and the original ethnicities of the children were kept intact.
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