Which events in 1917 the united states decide to enter world war i?

The assassination of Archduke Franz Ferdinand of Austria, and also the Nationalism and militarism. 

Germany resuming unrestricted submarine warfare is one
The Zimmerman Telegram's interception when Britain said Germany sent Mexico a note to attack us.

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.