The promise by Germany in 1916 to stop sinking merchant ships without warning?

The international rules of war...and yes, there ARE rules of war!.. in 1916 were that submarines had to surface, ask a ship to stop, send over a crew in a small boat, examine the ships papers, and then decide if it was OK to sink the ship after the crew had been given a chance to abandon ship. As you can imagine, this didn't work too well, and Germany was losing WW1 because it was blockaded by the British Navy and couldn't do much about ships bringing supplies into England under the rules above. Every time the Germans would start sinking ships without warning, the US would protest, and to keep the US out of the war the Germans would modify their behavior for a while. Eventually they realized they were done if they couldn't stop the British from importing what the British needed, so turned to unrestricted submarine warfare and that brought America into the war. It is also to be noted that, 22 years later when WW2 broke out, US, German, Japanese and British subs never even pretended to do the stop and search routine but just fired away from the beginning.