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They used drummers to keep the soldiers marching at the same pace.
Nebula, after having played the games, I am more than confused at your explanation. I will do a less confusing job.
There is this magical machine called the Animus. It allows a user to experience and interact with an ancestors memories. Evil people called the Templars (or Abstergo) kidnap some guy called Desmond, they put Desmond in the Animus to view his memories of some bloke called Altair, who is an assassin.
That's basically how they do it.
Also again Nebula, they only do "important" or interesting historical periods, where "good" and "evil" can be easily seen. I wouldn't be too surprised if one was set in Stalinistic Russia.