I think you are indeed a bit confused. Deductive reasoning is equivalent to Natural Deduction, where starting from an axiom or a theorem you can deduce, via rules of inference, another theorem. Now, this is on a purely syntactical level, that is, we are not concerned with the truth of the theorems. An argument is said to be 'sound' whenever the premises are true. Notice that here we are claiming something about the semantic conditions of the premises.
Now, I don't really think that history is concerned at all by deductive reasoning but it is definitely studied on its own. Actually is at the core of the study of formal logic.
Consider the following argument:
All human are mortal,
I am human.
Therefore, I am a mortal.
All human can fly,
You are a human.
Therefore, you can fly.
Now these are both instantiation of the rule of Modus Ponens:
A implies B
The argument I) is sound, while II) is unsound. But the conclusions logically follow from the premises in both, that is to say, whenever all the premises are true the conclusion must be true.
This is the semantic definition of Logical Consequence, the semantic and the syntactic notion of 'follows from' are equivalent only in those Logics that are complete, that is, those in which all and only the theorems are true. Arithmetics is incomplete, this was discovered by Goedel, hence it has more truths than the ones that are provable.
Hope this helped!