Solving this problem - no, challenge, there are no problems - was the refugee camps.

This seems to be a bit of confusion with subject-verb agreement. The subject here is actually 'refugee camps,' so we need a plural verb - 'were' instead of 'was.'

Source: World War Z, p. 139

Edit: This, and many other errors in the book, may be attributed to the oral nature of the text, that is, it purports to merely record the words spoken by the individuals interviewed. However, I believe this is not the case in this instance, as the individual in question was a (presumably) highly educated, high-ranking government officer.