We almost always assume that an ET race will have equal tech in war fighting as they do in space travel. That's a human-centric thought process. We assume it because it's how we would be, nothing more. I posit that we are unique in the universe because of our violent tendencies and that we could very well overwhelm a technologically superior for with the savagery of our attacks. It's quite logical that an advanced ET race would never comprehend something as dramatically stupid as a shahid martyrdom.
You ever watch Falling Skies, by chance?
They could drop kick the U.S economy in a heart beat if they elected to.
And who is gonna by their cheap stuff?
Or their services. I read somewhere that on some packages of fish, it will read caught in Canada, filleted in China...and then it's ship back here. So, you have have many parts of their economy that is dependent on US/North American industries.
Sinking our economy would sink theirs. Plus, you have a lot of rich Chinese that have to have their Western goods. If the US tanks, you have a lot of rich folks really pissed at their own government. Which means focus and money could be turned towards them.