I have been messing around on Fold3.com and came across declassified military intelligence files titled “Negro Subversion”. Many of the files point to informants (is that the right word?) discussing collusion between German immigrants and descendants of slaves working together to overthrow the US government. The files discuss things like: a German American shopkeeper expressed sympathy for the plight of the Negro, thus that shopkeeper must be watched closely. Or: a German American man was seen commingling with a group of Negros talking about rights and liberties, therefore requiring further investigation.
To me, there didn’t seem to be much veracity to the claims. Most, if not all, of the investigations turned up nothing. I am wondering if this was a widespread fear in the US government/military? Is there any scholarly work on this? I couldn’t find anything.
This is my first post in this sub! I’m excited for any response.
No, there isn't. There is no evidence pointing towards any potential co-operation between African Americans and German Americans and/or German agents.
Yet that does not mean that the fear wasn't real amongst white Americans. The period of the First World War in the United States was an era of hypernationalism through which any and all dissidence against the war was seen as highly objectionable (and often struck down by all means necessary). Loyalty to the United States and the choices made by its government was therefore expected. But could the African American community be expected to be loyal to the United States? Wartime paranoia made white Americans suspicious of possible disloyalty of several minority groups, yet the suspicion of African Americans was clearly based on racial fears of a possible race war orchestrated by Germans. This was not only believed by ordinary Americans who provided the paranoid reports that you mentioned in your post, but also by the United States government who throughout this period engaged in surveillance of the African American community. Yet nothing came out of it.
For the most part, African Americans were either ambivalent or supportive of the aims of the United States government during this period of time, with some prominent leaders co-opting the democracy discourse of Woodrow Wilson in order to proclaim that African Americans would be loyal to the United States -- in exchange for civil rights, justice, and democracy. This was most evident in the symbolic figure of the African American soldier, seen as the 'torchbearer of democracy', and whose sacrifices on the Western front was meant to usher in a new era for African Americans in the United States.
Yet simultaneously, there were African American dissidents. Yet unlike the racist and paternalistic idea of African Americans having to be guided by a white German hand, these were individuals who had their own agency. People like antiwar activist and socialists A. Philip Randolph and Chandler Owen. Randolph and Owen were editors of The Messenger, a socialist newspaper that loudly spoke out against the war (something that had been criminalized by the Espionage Act and later the Sedition Act). During one stop of their anti-war tour in 1918, the duo were arrested and brought before a judge who promptly dismissed them since he believed that African Americans could not have produced such a sophisticated newspaper -- they must have been guided by white socialists. Released, they continued where they had left off, undeterred by the possibility of being arrested again.
For scholarship on this topic, see Race, War, and Surveillance: African Americans and the United States Government during World War I by Mark Ellis (Indiana University Press, 2001). For a general overview, see Torchbearers of Democracy: African American Soldiers in the World War I Era by Chad L. Williams (University of North Carolina Press, 2010).