An example of this is the exclusion of the United States as a possible adversary from British planning before both world wars. A paper prepared in 1928 for the CID stated that "[t]he improbability of war with America has been a factor in the policy of this country for a considerable number of years." It further acknowledged that the consequences of a conflict with the United States would be disastrous to British interests. Foreign Secretary Sir Austen Chamberlain observed that such a conflict was beyond reasonable expectations:
It would not even be necessary for the United States to take any warlike action against us in protest. They could close markets and financial sources of vital importance to us. Such a situation [was] the only one from which a war with America might arise, but he could not imagine that any British Government would be mad enough to create such a position.
Asserting that war with America was implausible played far more than just a passive role (i.e., excluding conflict with the US from military scenarios) in British planning. When the consolidation of the Royal Navy followed the introduction of reforms in the early years of the 20th century, there was only limited concern expressed about the reduction of naval assets in North American waters. Whitehall was also guided in framing its relations with other countries by that outlook. The Anglo-Japanese Arbitration Treaty (1911) included a clause that released Britain from its alliance obligations should Japan find itself in a conflict with the United States.
The imposition on strategic planning of this assumption was probably influenced by a variety of nonrational considerations, such as the wrongness of a conflict between the two principal Anglo-Saxon powers. It was, after all, a leading British politician, Joseph Chamberlain, who in 1896 referred to an Anglo-American war as an "absurdity as well as a crime" and opined that the two countries would one day work together to fashion a new world order "sanctioned by humanity and justice." Just as significant, however, this presupposition was also firmly grounded in a rational appreciation of Britain’s vulnerabilities and its strategic interests. As that assessment demanded that conflict with Washington be avoided, there was no purpose served in planning military contingencies against the United States. The [Committee of Imperial Defense], and presumably lower-level defense planning staffs, were instructed to assume that no such conflict would occur.Recognition of imposed assumptions in the strategic planning process is just one of several ways that the strategist can remain cognizant of the inherently political nature of his work. If policymakers say we're not going to war with China and it does us no damned good to prepare for war with China, then that's the way it ought to be. The strategist's assumptions must be based as a matter of course on the nation's assumptions. But this can get complicated in what's probably a pretty obvious way: in a republic, no one person or body gets to decide what constitutes the national interest. Whatever your feelings about war powers or the constitutionality of military action absent legislative sanction, it's clear that the American system of government includes a role for both the Congress and the President in both foreign policy and warmaking. (The plain fact that these two domains of state action were far more clearly delineated from one another in the 18th century than the 21st -- and that the erosion of this line complicates matters -- hardly even bears mentioning.)
When it comes to national strategy, is it even possible for the executive to provide direction to his military planners based on a policy determination like the one discussed above? Could the president direct the Pentagon to exclude China from planning scenarios in a country where the Defense Department has a statutory requirement to brief Congress annually on Chinese military strength? Or where it's considered appropriate and unexceptional more generally for the Congress to legislate requirements for all sorts of similar reports and associated preparatory measures? (For example 10 U.S.C. §153(b)(2), which requires the Chairman of the Joint Chiefs of Staff to submit to Congress in odd-numbered years "an assessment of the nature and magnitude of the strategic and military risks associated with executing the missions called for under the current National Military Strategy" (which, lest you forget, is published by the CJCS himself).)
I suppose the answer is that it's still perfectly reasonable for the White House to lay down its own imposed assumptions within the confines of each administration's four-year strategic planning cycle, but the threat of Congressional squealing about anything controversial mitigates against such definitive pronouncements. (I should note here that I'm only using the China example as a thought experiment, in large part because I found it difficult not to think of our creditor-frenemy when reading Chamberlain's remarks about closing markets and governmental madness.)
Is it too hard to do realistically constrained, scenario-based strategic planning in a non-unitary government with four-year turnover? Is this what Olson meant when he said we lacked the necessary "strategic culture" absent the Cold War?