The United States elected to enter World War I because unrestricted submarine warfare had led to attacks on the US shipping vessels, and the conflict threatened the economic interests of the country abroad. The 2nd option is the right answer.
Explanation:
The United States entered World War I in 1917 after two and half years of its beginning in 1914. With the interest to keep the US out of the European conflict and strong isolationist sentiment, President Wilson had adopted a position of neutrality. But a German U-Boat caused the sinking of the passenger ship the "Lusitania" and six other American merchant ships including the Housatonic without any warning. Additionally, the "Zimmerman telegram" was expropriated promising the Mexican Government that Germany would help Mexico in recovering the territory it had surrendered to the US after the Mexican-American War. These reasons compelled Wilson to declare war against Germany in 1917.
