Sure, always good to have military input from the coal face, but that is distinctly different from an officer on the ground, deciding to back X group against another or to reverse a policy already in place. Best he can do, is to argue his case and then act when instructed to do so, his plans first having been scrutinised by the diplomats. Historically the best I can offer is the difference between Allenby's success in the Palestine campaign, versus MacArthur getting himself sacked in Korea.
Again Wilf, a military officer serviing in a country team as an attache or a security assistance officer is a diplomat. As for backing a group, that is another decision that can be made at the local level if it is done so under a general policy umbrella.

There are varying degrees of influence and decisionmaking authority accorded officers serving in such positions depending on country, crisis, and national interest. In the larger countries that would be much less than you would find in Africa or Latin America. It tends to be a case of management by exception; the framework is established and you make the decisions within that framework. If once Washington hears of those decisions, they accept, you are good. If not, then you may face recall. But if you believe that every single decision is vetted and scrutinized by a panel of policy makers, you are mistaken. It does not work that way, nor should it.

Military Force is for the breaking of will, not the building of nations.
That makes a nice neat slogan, Wilf, and I know you like to repeat it. It bears little resemblance to the reality of the Congo, Iraq, or Afghanistan.

We will have to agree to disagree.

Tom