How many soldiers have died in wars throughout human history?

It is an indeterminable amount. The reason is that war, in the modern context, goes back as far back as human history, both written and unwritten.
And due to the lack of written history, at certain points, it cannot be determined.
Additionally wars may be fought as small as clan or tribal disputes. These being so small they only may get a single line in a history book.

First answer:
Trillions.
In the Gallipoli campaign alone:
8,709 Australians
2,701 new Zealanders,
1,594 Indians
9, 874 french,
21, 255 British
86,700 Turkish died.

And that was only a part of the war.