Many of these factors could not be simply controlled by a few men, no matter how much power or authority they have.
Okay, then I expect to see those factors explained as such in the essay... I'll keep reading...
Although they had a great deal of power, they were still influenced by what the citizens and
what other government officials
thought about the war.
I'll add a semi-colons so that it is not a run on sentence:
All of these countries had good motives for a war; therefore, it is illogical to place the blame just upon the leaders of those countries, rather than analyzing the circumstances that made the countries want to wage war.
Okay, somewhere in the essay you should acknowledge what he actually means: that it could have gone a very different way if a few individuals had made different decisions -- that the few decided the fates of many. YOU have argued that many contextual factors were influential, but you have not really shown that the leaders did not have the ability to make a crucial decision.
Maybe you just need to tweak your thesis to acknowledge the part of his argument that you accept.
The essay can only support the argument you are making if you talk about the mechanisms of government, the kinds of authority enjoyed by each leader involved in what was to become the war. Well, no you really don't! You just have to acknowledge the part of what Stoessinger is saying that is reasonable to prove that you did not miss his point!
I am afraid I am not making sense.
:-)