One of the reasons the nited states is often frustrated in foreign policy issues is that military power is no longer the primarty instrument of foreign policu

That statement is true.

For example, in dealing with issues with North Korea.

If we're approaching it with millitary approach, we can finish the dictatorship in that country with one single missile.

But, we can't do that because we cannot sacrifice the lives of millions of innocent people, so we have to choose the hard diplomatic path.