Foreign Policy in my opinion is purely about economics. Global Policy is about human rights, multilateral action, and global security.
Defense is a purely domestic issue. It is not any one nation's right, or role, or obligation to be responsible for or take unilateral action against another sovereign nation no matter what. That's the role of a global league of nations. Which means that defense is about protecting your own citizens from harm, not from proactively endangering or attacking any other nation or its citizens.
So Foreign Policy = Economic Policy.
If you've been living under a rock, you'll disagree with me. Otherwise, you will have no doubts about this. The American mortgage crisis has become a planetary crisis, and are you ready for this? One that has resulted in the US Dollar actually rising against the Euro, Pound, Yuan, Yen, etc. Why? The interrelationships between every economy are now more profound than ever, it manifests itself in banking, manufacturing, health care, pharmaceuticals, defense, transportation, you name it.
Foreign debt and balance of trade/payments are in my opinion irrelevant measures.
Why? Because there's no real difference between foreign and domestic anymore! Everyone's worried that China holds too much American debt, and that gives them some kind of hold over the American economy! But what can they do? Foreign ownership means that that entity is now deeply vested in your future - their success is now predicated on your success - talk about mutually-assured construction! <-- Maybe this should be the new world economy phrase:)!
There is no longer such a thing (especially for a country like the United States) as a local economic incident. So if a country is interested in declaring war against the USA, they end up (maybe even before the first casualties) potentially harming their own economy before this one! They will absolutely also affect other economies and nations that they trade with, have pacts with, and might even ally with. And all of these nations will visibly hate the idea of getting caught in the collateral damage. Unless a country is prepared to throw itself under the bus (literally cut off its nose to spite its face), to oppose another country, there is no point, value, or benefit to going to war.
This begs the question - "what about those countries that have nothing to lose?" Excellent question:) This is why economic policy and foreign policy are so intertwined. It is in the best national defense interest of every nation that has, to make sure every other nation in the world and every citizen in the world also has. This is not global philanthropy - this about global investment, global returns, and global opportunity. Building the infrastructure for the planet, making education, health care, and food available to everyone, and then going on to building roads, buildings, power plants, etc. are what every has economy should do as a matter of national defense.
Give everyone on this planet something to lose, and everyone on this planet will be more worried about protecting, preserving and growing their lot in life and less worried about being vindictive or bearing animus against anyone; they'll instead focus on and be excited about their children's futures, and there will be a smile on their faces.