When did america become involved in world war i?

after the assassination of the austrian archduke
after the destruction of the battleship maine
after germany sunk the lusitania

After Germany sunk the Lusitania. It was a ship filled with American s=citizens, and was sunk under the impression that it was transporting supplies to Great Britain, which it was.

Actually, The United States became involved after recieving the Zimmerman Telegraph, a telegraph from Germany to Mexico. It detailed a Mexican American war, that promised Mexico all its land back. Including NM, TX, and AZ. Granted the telegraph was the straw that broke the camel's back, and out of those three options, i would definetely say the Lusitania