Hello. I am an adjunct professor with a Master's Degree in Holocaust and Genocide Studies. I hope to be able to address your question but that involves showing how there wasn't an issue.

The thing you need to remember when we discuss The Holocaust is that you can't come at every issue from a contemporary standpoint. This is one of those issues. Concentration camps is a dirty and evil concept tainted with thoughts of jackboots, atrocities, and Nazis because of The Holocaust. At the time, it wasn't really an issue per say.

If the moderators do not mind the use of a tertiary source to illustrate a point, the concept of a "concentration camp" entered the Merriam-Webster dictionary in 1897.; thirty-six years before opening of Dachau - the first Nazi concentration camp. Journalist James L. Dickerson chose to use the term in the context of the Cherokee removal under General Winfield Scott in the late 1930s (Dickerson, 29-30). As an Americanist genocide scholar, I agree that the term should apply to numerous indigenous internments including the Sioux at Fort Snelling in the aftermath of the genocidal Dakota War of 1862 (Carley, 78). Then there were the camps in Cuba during the Spanish-American-Cuban-Filipino War, the camps utilized by the British during the Second Boer War (Warwick, 145), the use of camps in German Southwest Africa which imprisoned the Herero and Nama (Schaller, 52) as well as other examples throughout the later 19th and early 20th century. Even in the era of Second World War, not only did the United States interned Japanese, German, and Italian-Americans as a result of FDR's Executive Order 9066, but they also forcibly interned the nearly nine-hundred Aleut Alaskan Natives as well. Concentration camps were not a dirty word prior to the Holocaust (and many camp systems persisted) and thus there was no real outcry when word of mass imprisonment came out of the Reich.

One notable example of an international response, however, came when the Red Cross inspected the "model camp" of Theresienstadt following the mass deportation of Danish Jewish. The inspection came in June of 1944 but it was largely a hoax perpetrated on the international community to hide the realities of the on-going genocide. There is a pretty good overview article by the United States Holocaust Memorial Museum. Most of the worst realities did not come to light until liberations late in the war and post-war materials from survivors (etc.).

In short, there was no response to any accusations (that I know of) because there was nothing accusatory to say since internment/concentration camps had become commonplace among empires. On top of that, the Red Cross failing to look further than the "model camp" helped hide the crimes until the end of the war.

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Work Cited:

Carley, Kenneth. The Dakota War of 1862: Minnesota's Other Civil War St. Paul: Minnesota Historical Society Press. 1976.

Dickerson, James L. Inside America's Concentration Camps: Two Centuries of Internment and Torture Chicago: Lawrence Hill Books. 2010.

Schaller, Dominik J. "Every Herero Will Be Shot": Genocide, Concentration Camps, and Slave Labor". In Forgotten Genocides: Oblivion, Denial, and Memory, edited by Rene Lemarchand. Philadelphia: University of Pennsylvania Press, 2011.

Warwick, Peter. Black People and the South African War 1899-1902 Cambridge: Cambridge University Press. 1983.

Further Reading:

Pitzer, Andrea. One Long Night: A Global History of Concentration Camps New York: Little Brown and Company. 2017.