It was tough being a German immigrant during World War I in the United States. Any support or sympathy for Germany was frowned on and possibly investigated by the government.
Before it was called the FBI, the Bureau of Investigation (BOI) investigated real and perceived threats to the nation and its citizens. Files from these investigations can be found on Fold3 in the FBI Case Files. They include tales of espionage during World War I, case files for German aliens who were politically suspect, records pertaining to Mexican neutrality, and reports dealing with alleged violations of federal laws.
Among the interesting investigations in the collection is a 418 page file on William Randolph Hearst that begins with this letter from an anonymous, “American”
Was someone in your family investigated by the BOI? Search the collection to find out.