Russell begins "Science and War" with a brief historical account of the increasingly intimate link between science and war. He cites examples from the Classical World and then the Renaissance. As Russell quickly brings us to modern warfare, he notes that while there are still noble soldiers fighting for causes they believe in, modern war is more about technology than those gallant fighters or their causes. Russell thus dispenses with the romanticizations of the glory of noble soldiers and brings the reader to the industry, machinery, and weapons of modern war.
When Russell begins to talk about how modern warfare is beginning to change, he starts to invoke his own opinions, and it becomes more like an editorial than a history. The essay started out as a kind of brief history: of the link between science and war. But, as he goes on and comes to modern war and his fears for the future, Russell switches from a historical narration to the "I" of a personal or political essay. From this point on, it is Russell's opinion rather than a historical account. It is also from this point on that Russell's essay becomes a warning, a didactic (having a motive to teach or instruct) tone.
This shift in tone to a more personal, didactic essay also has an element of the manifesto. Russell also invokes the "we" that is characteristic of "we the people" or the people who must mobilize to form a cultural movement. Russell is trying to rally the troops, so to speak, to abolish any notion of a catastrophic war. Russell ends the essay pessimistically (his personal fears, using his editorial "I") but he does try to rally his readers by invoking the communal "we" in hopes that he will be mistaken in his pessimism.
Either we must allow the human race to exterminate itself, or we must forgo certain liberties which are very dear to us, more especially the liberty to kill foreigners whenever we feel so disposed.
We must learn not to say: "Never! Better death than dishonor." We, must learn to submit to law, even when imposed by aliens whom we hate and despise, and whom we believe to be blind to all considerations of righteousness.
In general terms, this is an essay because it is largely constructed around the author's thoughts and beliefs.
Thank you so much. I have an exam tomorrow and was stuck with this question.