system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does one man manage to convince the idea of the Holocaust to an entire army, consisting of fully functional human beings, capable of making rational decisions?

Serious question. In my country, we only learned about a page or two about the World War I and II, and nothing about the Holocaust (I swear), so I never fully understood them or why the things that happened, happened.
gpt
Imagine you're a soldier. America has just rebounded from getting its ass kicked on the global stage. A new leader comes along, promising to be better than the last guys. You're desperate. You vote him in.

He's great for the country. He expands private gun ownership, and has the country looking like it's about to prosper. Your family is doing better than it was before the war. You don't feel the incessant need to stand on guard, for fear of war breaking out again.

This new leader tells you that everything would be perfect if you just dealt with this one group of people. For the sake of this comparison, let's say they're Arabs. You don't have the education necessary to understand that the claims about them poisoning water and planning a revolution aren't true. You figure it's going to be as simple as moving them to a different neighborhood, to keep an eye on them for a while.

It starts with relocation. Then the government decides to take away their guns, along with their ability to congregate. You're convinced these are small things. 

All of a sudden, you start seeing the people around you getting vicious toward the Arabs. They can only really explain their hate by saying that "they're ruining the country, they need to be taken care of". You question why they're so violent. You start to hear whispers of you being "unpatriotic". You give in and join in the chaos.

Soon, the leader decides to move all of the Arabs to a work camp. Again, you're not sure you're on board with it, but the rapidly increasing numbers of your friends, neighbors, even relatives that are for it drives you to fall in line with the beliefs; after all, how can thousands of people be wrong about something so big and serious?

Soon, the leader is ordering executions in the camps. At this point, you're completely against what is going on, but you're surrounded by an army approaching 10 million people. If you speak out, you'll be shot. If you don't do your duty, you'll be shot. Your family is in constant danger. You're being watched. So you fall in line and do what you're told.