While practitioners of and believers in of Realpolitik believe that military force (and its cold, self-interested use) is the final determining factor in a geopolitical contest, they and their fellow-travelers often forget that this factor is less meaningful in the long-term than those aspects of "soft-power," such as culture, law, trade and the like.
Obviously realists have a point when they say that raw tangible power, order and influence are of greater proximate importance than those aspects of soft-power. Without power, order and influence, things like liberty, prosperity, culture cannot exist. Art cannot flourish, cosmopolitanism ceases, the free exchange of ideas and philosophies, commodities and goods---they all come to an end. Poetry and jazz didn't cause the downfall of fascism. That said, the democratic world's shared liberal cultural values enabled them to politically unite in such a manner so as to allow them to bring proper military and economic power to bear against the Axis. Without culture and values, there wouldn't have been a differentiation between the Axis and the Allies, between the Communists and the Free World, or even today between the forces of Order and those of Islamic militarism.
Military power counts in the "last instance," yet it is but one of many tools which states and civilizations can use in their pursuit of power, order and influence. As Clausewitz says, "war is politics through other means." Military force is an important tool, and when used correctly can have an amazingly decisive impact. Sometimes these impacts are of world-shattering importance with long-term civilizational importance. More often, its importance (while decisive) is only in the short-term, due to the greater importance of cultural, economic, political and legal factors which almost always have greater long-term influence on the trajectory of a civilization than military power alone.
My historical and political studies tell me that the most important long-term sort of power is cultural. It has a gravitational force all of its own which military power can complement, or rescue from stalemate, but never truly replace. The Roman Legions conquered much of the Mediterranean world, but the Roman Empire would not have lasted as long as it did had it not been for Roman laws, Rome's fusion of Italian and Greek-Hellenistic culture, its cosmopolitanism and pantheistic approach to religion and ethnicity. When the ethnic and religious diversity of the Empire became so extreme that the differences of Rome's subjects were far exceeding any sense of commonality among them (thus fueling the fires of tribal separatism, independence movements and anti-Roman sentiment), Constantine adopted Christianity as the official state religion and imposed it upon his tens of millions of subjects. As a result, an inhabitant of Wales could travel to Egypt for trade, and be welcome with open arms due to the common cultural practices, religious rituals and ecclesiastical rules regulating commerce which bound the Empire together.
Governing and ruling an empire (indeed creating an empire) often rely on force, and force settles the final questions of sovereignty and power. But that power will not last very long without cultural support. We saw this with the Mongols---they conquered the greatest empire in world history, laying waste to countless peoples and cultures and committing genocides of a scale not seen until the 19th and 20th centuries. Their armies were practically invincible and were only defeated a handful of times in battle. And yet, despite this, their empire crumbled rather quickly after the death of Genghis Khan. They left no long-lasting cultural, commercial, architectural, civic-improvement, artistic, literary or religious legacies that bound the peoples of Mongolia with with those of China, Central Asia, the Middle East, Russia and Eastern Europe. Rather, the various Khans became subsumed by their subject populations, assimilated into the superior "soft power" of a dozen conquered nations. Kublai Khan may have ruled China, but China conquered him more than the Khans conquered China. The lesson here is clear: without a compelling cultural influence, your quest for global leadership is for naught. Domestically, too, the governed cannot purely be compelled to obey by way of force alone---this is too vulgar and ineffective a recipe for public tranquility. Rather, there needs to be a cultural, philosophical, intellectual rationalization--commonly held by the people---which legitimizes the state's utilization of such sovereign authority. A judge can enforce the law and impose a sentence, but if the culture disagrees with the legitimacy of said law or sentence, tranquility and order will be upset. U.S. history is rife with examples where the legal system failed to keep pace with cultural understanding, causing chaos and instability. A good example of this is when, in the 1850s, northern states were becoming increasingly hostile to southern slave-interests and the Fugitive Slave Law, which compelled northern authorities to use northern money and manpower to apprehend southern slaves. Aiding and abetting runaway slaves on the Underground Railroad became a federal felony offense. That said, northern juries refused to enforce the law and northern populations refused to assist southern interests. Law & Order, in effect, are meaningless without sufficient cultural support.
The example of the rise and fall of a common French culture in Europe is fascinating. It has been discussed by historians like Toynbee, Huntington and Kissinger, in analying the importance of cultural power in extending national influence, and how military heavy-handedness can ruin a nation's cultural influence and ultimately, its power.
Throughout the Renaissance, Enlightenment and up to the mid 19th century, French language and culture was seen as the ultimate mark of culture and sophistication throughout much of Europe. England may have bested France in countless wars, but the English were small in number, despite their commercial and military prowess. France had a larger population and a rich cultural history and influence that were the envy of many of her neighbors. By the mid 1700s, the majority of the courts of Europe spoke French and used it as a lingua franca for official political communication and courtly conduct. French was in the process of replacing Latin as the official language of science and academia. Granted, France was a very rich and powerful nation and had a mighty military, which often won wars (but also lost wars), but almost always seemed to bounce back from defeat to reclaim her rightful place. And her ability to bounce back was due to her cultural strengths and influence.
All this came to an end with Napoleon, whose hubris and ambition for a continental empire destroyed Europe's love affair with French culture and the French language. During the late 1700s the Russian Czar, Austrian Emperor, and many of the electors of the Holy Roman Empire---including Prussia and it's notorious Francophile, Frederick the Great---insisted on conducting all their business in French. Palaces were given French names. French style and dress, food, philosophy and customs were imported as the mark of civility. Prior to Napoleon, the works of Voltaire and Rousseau were spreading throughout Europe and monarchs were slowly starting to reform their systems, due to this passive form of cultural diffusion and Enlightenment influence. Even rustics living across the Atlantic Ocean, in Britain's American colonies were increasingly under the influence of French culture and philosophy, much to the ultimate chagrin of the British Empire. French soft-power was extending French influence in a way the armies of Louis XIV never could.
All this came to an end in the period between 1789-1815 when the regimes of the French Revolution and Napoleon dramatically and violently threatened the continent's political, economic, cultural and social tranquility. Regicide, anti-clericalism, expropriation of Church lands, imprisonment of the Pope, a decade or more of brutal military occupation (along with widespread rape and pillage) and 15 years of unceasing, unrelenting total war caused much of Europe to lose its taste for all things French. Shaking off French shackles, the peoples of occupied Europe threw the baby out with the bathwater and waged a Kulturkampf on the French language, French cooking, French philosophy (especially of the Enlightenment sort), French republicanism, neoclassicism and the like. Replacing the void, there arose a wave of reactionary nationalism, antisemitism and ethnic romanticism---the ideology which fueled European resistance to French military occupation.
Prior to this period, Russia, Spain and the various states of Germany had, as a result of peaceful and non-intrusive French cultural influence in the 18th century been slowly moving toward greater civil liberties and enlightenment principles (by this, I mean the natural influence that language, ideas, books and music have on foreign peoples who willingly embrace it, rather than having it forced down their throats by way of foreign military occupation). Their experience with the French Revolution and Napoleon caused a political counter-reaction in these nations. Rather than continue down the path of embracing the reforms proposed by Rousseau and Voltaire, Spain, Germany and Russia banned these authors outright as subversive, rescinded vast swaths of previously enacted progressive legislation, and became bastions of provincialism, monarchism and reactionary fervor. As Newton told us, force often creates an equal and opposite counter-force. Just as it is with gravity and physics, so it is with politics.
The historical record is clear---French influence was greatest when France didn't force things down people's throats by way of bayonet. And Europe was better off when the French only used military force sparingly, in the narrow pursuit of her self-interest. The Revolution's and Napoleon's obsession with "Wars of Liberation" and "Wars of Conquest," ended a 300 year reign of French cultural supremacy.
America today has amazing cultural influence. Hollywood movies and TV, books, universities, music and the like---it's the envy of the world. The newly emerging middle class in places like China and India, Africa and South America embrace much of American culture. They learn in our universities and they import many of our ideas back to their homelands. In many ways, this is what gives America strength.
Granted, the only reason this system of global influence exists is because we won WW2. But victory in 1945 only gave us the opportunity to create this system. Our ability to maintain it depends solely on our ability to remain a shining beacon, a "City on a Hill," that can be an example to the world.
If we embrace the sort of crass nationalism that seems to be in vogue at the moment, we will irreparably damage American power and interests throughout the globe. The military is important. Military solutions to certain problems must be given serious thought, of course. But we must not embrace a frame of mind which sees the military as a panacea---as the solution to all our problems, irrespective of their nature. And many of the nationalists we see today unfortunately have such a mindset, not realizing that in trying to help their nation, they will actually harm it.
Dominating and bullying others is not the best way to create or sustain long-lasting relationships. This is true for individuals, as well as nations. That said, believers in soft power underestimate the necessity of having a strong military, as well as the need to use it every now in then, provided its scope is limited, the objective narrowly defined. Liberals often accept the aggressiveness of authoritarians, but demand pacifism from democracies, and this, too, is unwise.
The great question, though, is can we have our cake and eat it, too? Or does pursuing one track invariably run you into opposition with the other? Are the two ideas mutually exclusive or inversely proportional?
Balance, as in all things, is key.