... then what is the difference between those and situations, as in:

how a person behaves in a given situation depends on those ideas (my bolds) ?

I can rephrase my entire comment substituting "system of ideas" for "situation", but that would be boring.

Now, if only ideas need to change, how does bombing cities and changing governments help? Is that not precisely changing a situation (slash "system of ideas")?

Bombing a weapons factory is not the persuasion of human beings to believe different things than they believed the day before the bombing. It may lead to people changing their ideas but it is not in itself the changing of ideas.

Is the priority in dealing with terrorism persuasion, or is it making persuasion more possible (which is what has happened in Iraq, with the replacement by force of the terrorist government that murdered people for dissent, with some kind of democratic system that allows for debate and therefore the growth of ideas)?

It seems to me that the difference between those two is the difference between pacifism and rightness. Not everything in the universe is theoretical. Planet earth would not cease to exist if the human race died out. And if everyone in Iran decided they wanted democracy, they would still have to depose the government before setting up elections.