system
Given the following post, respond as if you're commenting on Reddit:
human
[World War Z (book)] How did the US military clear the west coast while establishing the safe zone?

In the book, the US government decided that its best shot at survival was establishing a safe zone from the Rockies to the Pacific Ocean, because the zombies would have trouble following them over the mountains. But what about the ones that were already there?

There are some *massive* cities out west like LA, San Fran, and Las Vegas that would have been crammed to the gills with Zombies. The military hadn't perfected the anti-zombie weapons and tactics seen in the second half of the book, so how did they clear out the millions of zombies in those cities?
gpt
Presumably during that time the military developed its tactics that it later used to clear the rest of the US, but also it was probably a real bad time for the military members. Lots of figuring out that aiming for the head is key. Lots of using automatic weapons for semiautomatic fire aiming for the head rather than center mass, with overpenetrating ammo a lot of the time. Overwhelming force did work at Yonkers, just not *enough*. The army probably learned enough of a lesson there to figure out how to fight smaller battles more successfully and they cleared that way.