Why did Wilson
sacrifice his policy of neutrality to enter World War I?

Although during presidency campaign he wasn't supporting the entrance to war, the public opinion changed as three American ships were sunk by Germans, who offered Mexico a military alliance and territories this country lost in earlier wars with the United States.

Explanation:

He asked before the US Congress on April 2, 1917, for United States entry into the war, and four days later Congress approved it.  At that moment the United States army was rather small., but then they started calling upon volunteers.Yet United States entry into the war changed everything, with the arrival of 2.1 million United States soldiers one of the decisive factors for the outcome of the war.

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Sorry, took me a while to find the answers but hope this helps! :)