Most prayer involved sacrifice, yes.

Also, it's important to remember just how religious people's lives used to be. A lot of work we'd consider secular today were ritual activities for our ancestors which had to be done in the presence of the gods. Slaughtering animals (aka animal sacrifice) was one of those activities. So were meals.

Given surviving practices from other ANE descendant cultures it's possible they viewed killing as an impure act which required divine approval to be performed safely. So was the execution of humans, such as excess POWs/criminals etc.

The kind of sacrifice which required the total destruction of the offering (holocaust) was rare in European traditions. It mostly seemed to be a semetic thing. The jews in particular had rules stating that if any part of a sacrifice was taken, the thief would become part of the sacrifice.