In all fairness, you never specified that.
Who is "ourselves"? If by that you mean people in a certain geographic area that are forced to pay taxes to a government that made up those borders, then it's never self-defense. The government is made up of people. Countries are made up of people and land. The only place I own (besides the whole property taxes thing) is my own house. If my house is broken into and I know who is responsible and I decide to respond with violence, that may not be the best way, but I will weigh the pros and cons, and that's morally permissible.
And what about who did the attacking? In the instance of suicide bombers, there can NEVER be self-defense. Those responsible already died, there can be no restitution, and killing other people who may or may not have been in the same association as them is NOT justified.
The fact is, people in the government and military are only held accountable when people are willing to risk their own safety to leak war documents. That means even if you THINK a country was invaded in self defense, if you support that war, then you support every thing that comes out of that war, the shooting of innocent families, the bombing of basic sewage and water supplies, and the creation of a new underclass who has seen nothing but destruction and violence. The war is out of your control, COMPLETELY! So don't pretend that you can support the idea of the war without supporting the results of the war.