Eleanor says, "We are the origins of war, not history's forces, nor the times, nor justice, nor the lack of it, nor religions, nor ideas, nor kinds of govt..." How does it demonstrate the politics of feudalism?
What Eleanor is truly talking about here is who is morally responsible for war. She is saying that it is human choices that cause wars -- not outside forces -- and therefore human beings are morally at fault when wars happen. In addition, she is saying that wars are not inevitable -- they are things that people choose. As the Lion in Winter link below says
The implication of Eleanor’s statement is that wars are not inevitable occurrences, but are the result of human choices, and that, therefore, it is possible to choose peace instead of war.
As far as feudalism goes, this quote does make sense (whether she meant it that way or not). In feudalism, wars started because of the personal choices of the rulers. This is much more true in that system than in any other.
In the feudal system, wars were about the king (or queen) and his dynasty and possessions. They were not about the interests of his country. In those days, there was not yet really any concept of people being part of a country. Instead, they were subjects of a king. Their loyalty could change as the result of war.
When kings went to war, they did it for their own good, not for the good of their "country." That is, for example, why Henry was off fighting wars in France. They didn't do England any good, but they were (Henry thought) good for him and his honor and that of his dynasty.