Why did submarine warfare push the US into World War 1?

The German government announced unrestricted submarine warfare against ANY ship sailing into Allied waters would be subject to surprise attack. Along with the German sabotage of Black Tom island powder magazine in 1916, the sinking of the Lusitania with American citizens onboard, and the Zimmerman telegram (German foreign secretary) that encouraged Mexico to ally with Germany and Mexico would win bad the former Mexican territory in the US South West, lead President Wilson to call for war. There were additional reasons, but I feel these were the Big Four.
U Boats were causing havoc on the trade routes between the US and Europe by destroying merchant ships. One of the biggest factors was the sinking of the Ocean Liner "Lusitania" by German UBoats, of the 139 US Citizens on board 128 were killed. Also, when Germany began a Submarine Campaign against Britain President Wilson had previously stated he would hold Germany responsible if that were to occur.