Answer:
The barbed wire being so far away slowed enemy advances heavily due to having to crawl through it. Essentially making it a livestock killing pen.
Barbed wire being far out like I stated before made the enemy advance slow thus enabling the Americans to eliminate the enemy with ranged gunfire while the enemy had to crawl.
Key points:
Enemy's advance was slowed.
As a result of being slowed the enemy's gunfire was disabled.
