There is a good deal of controversy about reciting Hallel on days not ordained by ancient tradition. But there are at least some opinions that Hallel should be recited to commemorate dates of national salvation.
Considering that the Holocaust resulted in the deaths of 6 million Jews, predominantly Ashkenazim, but many Sepharadim as well, why don't we mark the Nazis' unconditional surrender on 25 Iyar, the Hebrew date of 8 May 1945, the effective date of Nazi surrender by reciting Hallel?