Why are Rex Tillerson, Donald Trump and the Republicans destroying the State Department?

The title question is fairly straight-forward and of crucial importance.  I am inspired to ask this question after reading the recent Politico article:  “PRESENT AT THE DESTRUCTION: HOW REX TILLERSON IS WRECKING THE STATE DEPARTMENT- I worked in Foggy Bottom for 6 years. I’ve never seen anything like this.”  

Many previous articles have detailed this on-going, odd, and alarming assault on the State Department and, by extension, on the Secretary of State position — one of the original cabinet positions, first held permanently by Thomas Jefferson.   This insider Politico article can be read as a useful, timely report on the alarming state of affairs:

While the lack of senior political appointees has gotten a lot of attention, less attention has been paid to the hollowing out of the career workforce, who actually run the department day to day. Tillerson has canceled the incoming class of foreign service officers. This as if the Navy told all of its incoming Naval Academy officers they weren’t needed. Senior officers have been unceremoniously pushed out. Many saw the writing on the wall and just retired, and many others are now awaiting buyout offers. He has dismissed State’s equivalent of an officer reserve—retired FSOs, who are often called upon to fill State’s many short-term staffing gaps, have been sent home despite no one to replace them. Office managers are now told three people must depart before they can make one hire. And now Bloomberg reports that Tillerson is blocking all lateral transfers within the department, preventing staffers from moving to another office even if it has an opening. Managers can’t fill openings; employees feel trapped.

The unanswered question in all these reports is why?  Why would Trump — and let’s be clear: all of the present Republicans — be so committed to decimating the State Department as an institution?  Candidly, I know this wasn't on my radar screen.  Of the many problems presented by a Trump/Republican win, I never thought: “Well, there goes our State Department.”

The author, Max Bergman, who served in the State Department from 2011–2017, doesn’t know the answer either.  He merely writes: “What is motivating Tillerson’s demolition effort is anyone’s guess.”

Well anyone . . . . what is your informed explanation?  Is anyone out there up to speed on this issue?  Is this something that has been festering in right-wing circles for years?  Is there a very specific answer, like oil, lingering neocon influence, or some other right wing bugaboo? Is there some sort of end-plan or goal that it is known but is being left unsaid in general press coverage?

Simply, does anyone have an informed understanding of exactly what Republicans are trying to do here, and why?