What event caused the establishment of the united states department of homeland security

It was the attacks on the World Trade Center in New York City on September 11th that caused the establishment of the United States department of homeland security, whose main objective is protect the US from terrorist attacks. 

The transcontinental railroad provided a means of fast transportation. it cut a 6 month trip into 6 days, created jobs for many people and encouraged immigration. the homestead act played a huge role in western expansion; it allowed settlers to begin a fresh start, and gave them land in exchange for their residence for up to five years and a small fee.