More than two and a half years, is the right answer.
Explanation:
The First World War began in the year 1914 in Europe. As many of the Americans wanted to stay out of the conflict so they supported the policy of strict and impartial neutrality announced by Woodrow Wilson, the then President of the United States. However, the United States engaged in the war due to the German policy of waging unlimited submarine warfare which resulted in the sinking of American ships. The Zimmerman Telegram was the recent cause of America's entry in the war.
