Our capitalist age has yet to displace war as the backdrop of history. Capitalism changed the nature and causes of war, but not the essence perceived by historian A. J. P. Taylor:

No matter what political reasons are given for war, the underlying reason is always economic.
Marx saw the French and American Revolutions as clearing the way for rational governance of the material potential unleashed by raw capitalism. Having concluded that capitalism would be nothing more than an interlude within our general progress toward socialism, he prophesied that the United States would be the most likely vehicle for accomplishing this transit because it was both the most dynamic and the most purely capitalistic of nations. This prediction tends to be cited in order to ridicule Marxist thinking, presumably because the United States would have become socialist by now if such a thing were ever to happen.

The outright dismissal of Marx as a student of USA phenomenology is, however, impossible. For one thing, it would be difficult to identify a more incisive contemporary interpreter of the American Civil War and its economic consequences. This war was of course no more civil than the Revolutionary War was revolutionary. Both were wars of session: secession from a monarch in the first case; secession from a social contract in the second. The Civil War is properly named only insofar as it continues the English Civil War, i.e.: the final conflict between New England's Protestant Roundheads and Virginia's Catholic Cavaliers.

Considered from the standpoint of the U.S. Constitution, one would have to say the South had a stronger case for leaving the Union than the North had for forcing them to stay.

North and South fought over means for supplying the manufactured goods requisite for settling America's western frontier, which might have been accomplished either by expanding industries in the North or by transshipping European goods through the South's geographically-favored ports.
Though slavery is often advanced as the cause this war, it is much more the case that war was merely the logical occasion for final resolution of an issue that was at the time being resolved peaceably all over the Western world. Fort Sumter was a customs house, not a slave market.
The South opened fire on a barrier to its prospective mercantile displacement of markets for the North's industries and to its agrarian export trade — not on opponents to the institution of slavery.
The ensuing conflict was tragic not only for the scale of carnage, which was far beyond anything that might have been anticipated by its instigators, but also for having instituted what might well be regarded as a second, inferior founding of the American nation. The first of these tragedies set the prototype for modern warfare, viz.: mechanized slaughter, total destruction of an adversary’s industrial capacity for resistance, terrorizing his population, and protracted military occupation in the aftermath. And yet America’s second founding might prove even more tragic in its continuing consequences.

Though history never tells us what might have occurred, dis-union could well have been the least attractive option available to President Lincoln. The indicia are that European Dynasts would have picked-off the re-confederated states as opportunities arose: we do know that Britain reinforced Canada at this time; France annexed Mexico; and the Tsar’s navy (in alliance with the Union) occupied the ports of San Francisco and New York, presumably to discourage mischief by Russia’s continental rivals.

Union was established over confederation in order to keep Europe’s economic interests, and their attendant dynastic politics, out of North America. Salutary as this result might have been at the time, it effectively reduced the states to administrative departments of a transcontinental regime, thereby removing state sovereignty as a check on central governance; and nothing has yet replaced this most essential constitutional provision for restraining the concentration of arbitrary power.

Capitalism was not absorbed by the state during the latter Nineteenth Century because the period’s leading political figures realized that states would be enhanced if capitalist intentions were given the fullest range of expression: taxing the results of free enterprise is more productive than appropriating the processes of enterprise. Marx admittedly saw little possibility for the capitalist oligarchs who emerged from America's western expansion achieving the good sense to compromise their Darwinian instincts. Thus he did not foresee their generally wise provisions for a sufficient general uplift to keep the masses quiescent, and even enthusiastic about their prospects under capitalism.

But the larger events of the Twentieth Century reveal a lessening of oligarchic command and control following their Gilded Age. Nascent America first blundered into European-style geopolitics by appropriating Spain's colonial empire during McKinley’s presidency; and became entirely smitten with itself as a world power under the influence his assistant naval secretary, vice president, and successor Roosevelt I. America permanently entered European politics when Wilson elected to tip the balance in der Kaiser's war for an economic free trade zone around Germany.

Unless one views the First World War as a Third War of Austrian Succession, it would be difficult conclude that this conflict accomplished anything beyond creating careers for Hitler and Lenin, i.e.: establishing that the response to a looming global depression would be a war between National Socialism and International Socialism. Lenin lived long enough to conclude that communization was not an effective way to organize the transition from a feudal, agrarian economy to an industrial economy. But socialism in some form would soon prove to be an effective organizing principle for all the wartime economies.

America's electorate (like their Weimar counterparts) freely chose a statist response to the economic crises of the 1930s; and socialism found such a popular embrace in the United States that its industrial barony launched at least one fairly substantial putsch upon Roosevelt II’s administration. Though International Socialism became the avant garde intellectual policy of the 1930's, Roosevelt II would eventually conclude, with Lenin, that economic command is a net material burden in peacetime.

Montagu Norman, ex-chief of the Bank of England, evaluated the experiment as follows:

with all the thought and good intentions that we provided … we achieved absolutely nothing. Nothing that I did and very little that old Ben [Strong, head of the US Federal Reserve] did … produced any good effect … or any effect at all. Except that we collected a lot of money from a lot of poor devils and gave it over to the four winds.1
Intellectual disaffection with economic command was rescued by Keynesian policy diktats that were taken up as an alternative Marxism:
Democratically elected political authorities would borrow oligarchic wealth that was not fetching much of a return on investment; and …
The borrowings would then be spent on a burgeoning federal establishment whose expenditures would somehow re-inflate demand for what the industrialists had to sell.
There is some likelihood that Keynes derived his policy from observations upon the Nazi regime 2 which, in any case, had both initiatives well under way a few years before publication of the General Theory.

But, where Keynes had advocated that government bury £5 notes in coal tips, Teutonic people emerged from the global economic depression by mortgaging their future to the acquisition of colonies in the territory of Slavic people. Germany would attempt in Western Asia what Britain (under a German royal house) had accomplished in Southern Asia two hundred years earlier.

Italy and Spain were Germany’s allies against international economic command; and France immediately capitulated to secure the military rear area for this operation. Stalin would soon request terms for a Soviet surrender. Britain was offered peace with a Germanized Europe that allowed it to keep its independence, its navy, and its colonies. This offer was emphasized by the Nazi's decision not to pursue their advantage at Dunkirk, nor respond to American naval provocations in the North Atlantic.

Given Britain's lack of war preparations, their refusal of peace would remain Quixotic until Roosevelt II could arouse an American appetite for war — which he only managed to do by means that were manifestly unconstitutional, and which some would call treason. Meanwhile, the war in Europe was settled by the unprecedented severity of the winter of 1942-43: the German gamble for an Asian empire was lost at Stalingrad.

Ostensibly, Anglo-American involvement in the European war had been dictated by Britain's mutual defense treaty with Poland — a treaty that neither signatory had any ability to enforce. Poland was taken off the map in simultaneous invasions by Hitler and Stalin, who had a prior, formal understanding as to how their prey would be divided. Legally, Chamberlain's meaningless declaration of war against Germany should have been paralleled by a similar declaration against Russia. Actually, Britain declared for Stalin and International Socialism against Hitler and National Socialism.

Poland (and much else) would disappear into a Soviet Empire in order to prevent the rise of a German Empire that might have rivaled the British. World War II, which ostensibly began with Poland’s division under the Molotov-Ribbentrop pact of 1939, ended with Europe divided between approximately the same interests at a line several hundred miles to the west under the Roosevelt-Stalin accords at Yalta in 1945.

Japan's bid for its Asian empire had been ruined somewhat earlier, at the battle of Midway in 1942. The issues of empire having been settled early in the war, World War II's confused aims then coalesced: the global industrial overcapacity that had caused economic depression would be liquidated by first bombing the industries, and then invading the territory, of both Germany and Japan. Further hostilities to attain this Carthaginian peace were sustained for the sake of the allies’ domestic political and economic harmony.

Capitalistic innovations in the areas of weaponry and tactics culminated in the nuclear detonations that compelled Japan’s ourtight surrender. There then emerged a consensus that no prospect of economic gain through war could justify the risk of a nuclear exchange; and war has since continued by a competition of forced obsolescence in the arsenals of one’s economic adversaries. This peace is uneasy; but it holds.
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1     Andrew Boyle, 1967: pp. 327-328.
2     John Kenneth Galbraith, 1977: pp. 213-214.