This articles details the philosophical issues surrounding war. The article is rather long, and many passages would be too intensive for high school students. Nonetheless, it does contain some very accessible passages and discussions.
The introduction offers a plausible definition of war, and outlines the philosophical questions surrounding the notion of war. Teachers might present students with this introduction, in an effort to get them thinking about whether they think war can ever be justified.
The section on Just War is very interesting. Just War Theory is likely to engage students, given its controversial nature. The article provides a nice explanation of contemporary just war theory. While it is not inaccessible, it is rather long. Teachers might pull out of this section certain passages or ideas and ask students for their opinions on them. One strategy that teachers might employ would be to present students with the 6 jus ad bellum (justice going into war) principles, and ask them whether they would subtract, or add, any conditions to this list. Jus post bellum (justice after war) is a relatively recent division of just war theory; teachers might discuss this with their students with reference to the US-led war in Iraq.