With our “war on terror,” we run the same risk of overestimating the power of a loose network of extremists, few in number. More dangerous may be our miscalculations about the significance of changes in warfare. A hundred years ago, most military planners and the civilian governments who watched from the sidelines got the nature of the coming war catastrophically wrong.

The great advances of Europe’s science and technology and the increasing output of its factories during its long period of peace had made going on the attack much more costly in casualties. The killing zone — the area that advancing soldiers had to cross in the face of deadly enemy fire — had expanded hugely, from 100 yards in the Napoleonic wars to over 1,000 yards by 1914. The rifles and machine guns they faced were firing faster and more accurately, and the artillery shells contained more devastating explosives. Soldiers attacking, no matter how brave, would suffer horrific losses, while defenders sat in the relative security of their trenches, behind sandbags and barbed wire.

A comparable mistake in our own time is the assumption that because of our advanced technology, we can deliver quick, focused and overpowering military actions — “surgical strikes” with drones and cruise missiles, “shock and awe” by carpet bombing and armored divisions — resulting in conflicts that will be short and limited in their impact, and victories that will be decisive. Increasingly, we are seeing asymmetrical wars between well-armed, organized forces on one side and low-level insurgencies on the other, which can spread across not just a region but a continent, or even the globe. Yet we are not seeing clear outcomes, partly because there is not one enemy but a shifting coalition of local warlords, religious warriors and other interested parties.

Think of Afghanistan or Syria, where local and international players are mingled and what constitutes victory is difficult to define. In such wars, those ordering military action must consider not just the combatants on the ground but the elusive yet critical factor of public opinion. Thanks to social media, every airstrike, artillery shell and cloud of poison gas that hits civilian targets is now filmed and tweeted around the world.

Globalization can heighten rivalries and fears between countries that one might otherwise expect to be friends. On the eve of World War I, Britain, the world’s greatest naval power, and Germany, the world’s greatest land power, were each other’s largest trading partners. British children played with toys, including lead soldiers, made in Germany, and the Royal Opera House in Covent Garden resounded with the voices of German singers performing German operas. But all that did not translate into friendship.

Quite the contrary. With Germany cutting into Britain’s traditional markets and vying with it for colonies and power, the British felt threatened. As early as 1896, a best-selling British pamphlet, “Made in Germany,” painted an ominous picture: “A gigantic commercial State is arising to menace our prosperity, and contend with us for the trade of the world.” Many Germans held reciprocal views. When Kaiser Wilhelm and his naval secretary Admiral Alfred von Tirpitz built a deepwater navy to challenge British naval supremacy, the unease in Britain about Germany’s growing commercial and military power turned into something close to panic.

It is tempting — and sobering — to compare today’s relationship between China and America to that between Germany and England a century ago. Lulling ourselves into a false sense of safety, we say that countries that have McDonald’s will never fight one another. Yet the extraordinary growth in trade and investment between China and the United States since the 1980s has not served to allay mutual suspicions. At a time when the two countries are competing for markets, resources and influence from the Caribbean to Central Asia, China has become increasingly ready to translate its economic strength into military power.