Ok first I have to make an assumption that your topic is about the balance between maintaining foreign relationships and keeping our nation safe (if this is a wrong assumption, please forgive me and move on!)
So here's my suggestion. Go for a role play. Make it real for them. They can easily understand and relate to the idea of balancing your own well being with the need to help others and maintain friendships or relationships. Give them friend based role playing to do, then make the association between that activity and the balance our nation has to maintain between its security needs and its foreign relationships. Pull out some foreign policy choices and ask their opinion on the choice? Did the government the right thing? Were they more concerned with security or foreign policy? If it were you, which would come first? How do you balance the two?
I think you can get your students to connect to how difficult this balance is because it relates to a similar balance they have to maintain in their own lives. I'm always a fan of the real life connection!
Something that just came up recently that ended up being pretty compelling was a discussion of the current state of our nuclear "deterrent" or nuclear capability. There was an article on slate.com about Harold Hering who was forced out of the air force for asking how he might verify that the order he received to launch was from a president acting rationally, etc.
The fact that we still maintain this massive nuclear arsenal that is waiting on only an order from one person led to a number of very interesting questions and discussions on the topic of national defense including the idea of deterrents, of maintaining a capability without necessarily using it, of conventional versus non-conventional warfare, etc. With my seniors I've also often tried to build the discussion from questions about how they would react to a draft since they are all of age or getting close to the time when they would be included.
Lastly, we had a great set of discussions and lessons about the question of whether our participation in WWII was justified or necessary or both. It isn't a question that gets asked often and the students were able to really push each other to determine what that question meant and to examine a lot of unexamined assumptions abotu the war.
I like to do case studies. For example, you could look at the war in Iraq or the one in Afghanistan. You could look at how those wars came about and how they affect America's security. By looking at how they came about and what their goals are, you could work on understanding the goals of US foreign policy. By looking at their impact on our security, you could work on understanding what is and is not possible in terms of protecting the nation. (For that last, you might contrast it with the times when wars were simpler -- like WWII -- and military force was more clearly efficacious in providing security.
Does that sound like what you're trying to accomplish?