Ok so the holocaust was terrible and concentration camps were even worse, and I understand the immediate purpose of concentration camps for Nazis, but I don't understand why this method was used. Everything I've read about the logistical nightmares of Germany fighting a multi-front war would make me think that they would want to be as efficient as possible in this endeavor. So why would they dedicate resources such as soldiers, trains, buildings, and supplies to keep these camps running instead of just using an immediate execution for their "undesirables"? Seems really out of character for an army known for speed and efficiency.