Why does zinn suggest are the real reason the u. s entered the war

The United States claimed the Lusitania carried an innocent cargo, and therefore the torpedoing was a monstrous German atrocity. Actually, the Lusitania was heavily armed: it carried 1,248 cases of 3 inch shells, 4,927 boxes of cartridges (1,000 rounds in each box), and 2,000 more cases of small arms ammunition. The British and American governments lied about the cargo.

- because the sinking of the Lusitania affected them for many reasons.