The 100th anniversary of the start of World War I was two days ago. Earlier this year I skimmed through a number of New York newspapers from just before the war and during its first few months. It is apparent how great a shock it was. The Christian great powers of Europe had been mostly at peace for nearly a century (though they had been gnawing at the Ottoman Empire), and suddenly they were embroiled in a vast continental war over a matter that from their perspective should have had little importance.
World War I began a rapid decline in free banking. None of the belligerents had free banking in 1914. In the United States, which did not become a belligerent until 1917, 1914 saw the Federal Reserve replace the previous system of government issue of currency alongside heavily regulated issue of notes by banks. The war and its aftereffects also disrupted the monetary systems of countries with free banking such that most adopted arrangements that gave governments a good deal more discretionary control over the monetary system.
There is a hole in free banking theory with respect to war. Free banking, like free trade more generally, is inherently a peacetime system. The question for its political durability is whether, like trade, it can be bent during wartime but prove sufficiently elastic to return to something like its old shape afterwards. If free banking is a peacetime-only system, politically it cannot persist, because war is an unfortunate reality of human existence.