Other than the Jews, who were the first victims of Nazi persecution?

From a chronological perspective, German homosexual men were one of the first victims of Nazi persecution. According to the U.S. Holocaust Memorial Museum, the Nazis stepped up their existing program of persecution against these men as soon as they took control of Germany in 1933. They persecuted them in a number of ways, like closing down homosexual organisations. (See the first reference link).

Two years later, persecution against homosexuals was further intensified when the Nazis narrowed the legal definition of homosexuality to include any "lewdness between men." The law also extended to the literary world: anyone found guilty of writing homoerotic fiction, for example, faced six months in prison. From 1936, homosexuals were routinely sent to concentration camps, like Auschwitz, where the vast majority were killed (See the second reference link).

For the Nazis, the practice of homosexuality violated socially and culturally-acceptable norms and values. Moreover, the Nazis knew that homosexuals were unlikely to have children and so they also threatened the country's population. It was for these reasons that homosexual men were mercilessly persecuted.