What promise did Germany make after the lusitania incident, and how did the promise affect U. S. manufacturers?

Germany promised not to attack merchant and passenger ships without  warning. U.S. manufacturers increased their trade with the Allies.

Explanation:

Germany introduced an untrained submarine warfare system, allowing armed merchant ships, but not torpedoes, without warning for passenger ships. Despite this beneficial limitation, the torpedo was fired without warning on the French cross-channel passenger ferry, Sussex, March 24, 1916 The ship was badly damaged and about 50 people were killed. President Woodrow Wilson has announced that if Germany continues this practice, the US will break diplomatic relations with Germany, even though no US citizens have been killed in the attack. Fearing the United States entry into the war, Germany attempted to enliven the United States by issuing it on May 4, 1916, Sussex pledged to change German naval warfare

The holy roman empire.