The American century shows no sign of ending
The rise and fall of great powers makes exciting history - all the more exciting if, as in the case of the Soviet Union, we can watch the spectacle unfold before our eyes. It is hardly surprising, therefore, that much of the discussion of the role of the US in the world is warped by the natural human desire for drama. The US is a declining power headed for collapse, says one side. No, says the other, America is the greatest empire since Rome at its peak.
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The truth is less dramatic but nonetheless fascinating: America's share of global economic power, and its potential share of global military power, have been roughly the same for a century and may remain so for another century or more.
A country's gross domestic product is a useful, though far from perfect, surrogate for its potential military power. According to the World Bank, in 2000 the US accounted for 27 per cent of the world's GDP. That seems like a lot, until you learn that in 1913 the US share was even larger at 32 per cent and larger still even earlier, in 1900 (38 per cent). As the American political scientist Robert A. Pape points out: "For the past century, the US share of gross world product was often double (or more) the share of any other state: 32 per cent in 1913, 31 per cent in 1938, 26 per cent in 1960, 22 per cent in 1980." At the end of the second world war, the US accounted for about half of all world manufacturing - but that was nothing new. As early as 1929, the US share of global manufacturing output was more than 43 per cent.
If the US had converted its economic potential into military power from the beginning, it would have been the dominant global power from the early 1900s onward. Americans deferred doing this as long as possible, in part because the US is a liberal, civilian society. In addition, in the early years of the two world wars, Americans hoped that Britain and other countries could restrain Germany with the help of US aid. Even in 1937, when Hitler's Germany spent 23.5 per cent of its much smaller economy on the military, the US dedicated only 1.5 per cent of its own GDP to defence. The moment that the US mobilised its gargantuan economy for war, however, Nazi Germany and Imperial Japan were doomed. Later, by devoting a relatively small part of its economy to defence, the US was able to spend the far more militarised but smaller Soviet economy into bankruptcy.
As the war in Iraq has shown, superior arms and money cannot guarantee victory in an essentially political contest. But it would be a mistake to conclude that the US is overextended. Since 2000, the US has ramped up its military spending from a little more than 3 per cent of GDP, not much more proportionately than France spends, to a little less than 5 per cent of GDP. This level of military spending is low by the standards of the Gulf war (6 per cent), the Vietnam war (10 per cent), the Korean war (15 per cent) and the second world war (35 per cent). Because the US economy is so huge, a little less than 5 per cent of GDP buys the US roughly twice as much military as the combined total of the Nato nations, most of which spend less than 2 per cent of national GDP on defence. If costs drop following the Iraq war, a policy of spending 3-4 per cent of US GDP on the military may be sustainable indefinitely, as long as the retirement costs of the baby boom generation are paid for by a combination of tax increases and spending cuts rather than by raids on the Pentagon budget.
What about the future? In 2050, China, India and the US are expected to be the world's most populous nations. The French International Relations Institute has predicted that by then, Greater China (China, Hong Kong, Macao and Taiwan) would be the leading economic power, accounting for 24 per cent of the world economy. North America (the US, Canada and Mexico) would be next with 23 per cent of world GDP. Goldman Sachs has also projected that by 2050, China will have the largest economy in the world, followed by the US and India.
But the rise of China and India will not mean the fall of the US. Instead, it will come at the expense of Europe, whose share of global GDP will decline, chiefly for demographic reasons. In some projections, Europe as a whole half a century from now will have fewer people than the US. If Goldman Sachs is right, the US, Mexico and Canada's share of global GDP in 2050, at 23 per cent, will be roughly what the US share of the world total was 70 years earlier in 1980, when it was 22 per cent. And per capita income in the US will be far higher than that in China and India into the 22nd century, if not beyond.
The relative size of the US in the global economy, then, may prove to be astonishingly stable over the 150 years from 1900 to 2050. Some neo-conservatives tend to underestimate US strength when they compare the US to Britain in the years before the second world war. Jihadists notwithstanding, the world is far safer today than in the 1930s. But in any case, the contemporary US should be compared not to Britain in 1937, with 10.2 per cent of the world's military power, but to the US in 1937, with 41.7 per cent of the total.
But supporters of US global hegemony would be mistaken to take heart from the underlying stability of America's share of world power. A country which over the long term is likely to account for about a quarter of world GDP can be first among the great powers in a multipolar world for generations to come. But an attempt to be the New Rome, by undermining economic strength with excessive military mobilisation, would most likely make the US the next Soviet Union.
The writer is the Whitehead SeniorFellow at the New America Foundation
美国世纪”并无终结迹象
大
国的兴衰写就了激动人心的历史，如果我们能亲眼目睹展现在眼前的奇观(比如苏联那种情况)，则更加让人激动了。因此，很多有关美国在全球地位的讨论，被人类“看好戏”的天然渴望所扭曲也就不足为奇了。一方说，美国是一个日渐式微、走向崩溃的大国。另一方说则反对说，美国是自鼎盛时期的罗马以来最强大的帝国。
事实没那么富有戏剧性，但仍然让人着迷：一个世纪以来，美国在全球经济实力中所占的份额，以及它在全球军事力量中的潜在份额，基本上没有变化，而在今后一个世纪或更长时间里，情况可能依然如此。
一个国家的国内生产总值(GDP)是其潜在军事力量的实用替代指标(尽管远非完美)。据世界银行(World Bank)的数据显示，2000年美国占了全球GDP的27%。这好像很多，但你要知道，1913的时候美国的份额更大，达32%。而在更早的1900年还要大(38%)。正如美国政治学家罗伯特?A?佩普(Robert A. Pape)指出：“在过去一个世纪，美国占世界生产总值的份额，往往是任何其它一个国家的两倍(或更多)：1913年是32%，1938年31%，1960年26%，1980年22%。”二战结束时，美国占全球制造业产出的一半左右，但这并不新鲜。早在1929年，美国占全球制造业产出的份额就超过了43%。
如果美国一开始就把它的经济潜力转化成军事力量，那么20世纪初以后，它早就成为占统治地位的全球大国了。美国人尽可能推迟这么做，部分是因为美国是一个自由、文明的社会。此外，在两次世界大战的最初几年，美国人曾希望英国和其它国家能在美国援助的帮助下抑制德国。即使在1937年，当时希特勒统治下的德国，将其规模小得多的经济中的23.5%投入了军事，美国则仅投入自身GDP的1.5%用于防务。然而，一旦美国为战争动用其庞大的经济，纳粹德国与日本帝国的末日就到了。后来，美国只将相对较小的一部分经济投入防务，就能够把军事化程度更高、但规模较小的苏联经济拖垮。
正如伊拉克战争所示，在以政治为本质的较量中，优越的武器与财力并不能保证胜利。但就此得出美国面铺得太开的结论就错了。2000年以来，美国已经把军费支出从GDP的3%多一点(比法国的军费支出比例高不了多少)，逐步增加到了接近GDP的5%。按照海湾战争(6%)、越南战争(10%)、朝鲜战争(15%)和二战(35%)的标准，这个水平的军费支出算是低的。因为美国经济非常庞大，用略少于5%的GDP为美国购买的军力，就大致相当于北约(Nato)国家加起来的两倍。大多北约国家的防御开支低于本国GDP的2%。如果伊拉克战争后开支下降，只要婴儿潮一代人的退休金是同时由增加税收和削减支出来负担，而非向五角大楼的预算开刀，军费支出占美国GDP的3%到4%的政策就可能无限期持续。
未来的情况会如何呢？2050年时，中国、印度和美国预计将成为世界上人口最多的国家。法国国际关系研究所(International Relations Institute)预测，大中华(中国大陆、香港、澳门和台湾)届时将成为主要经济大国，占全球经济的24%。北美(美国、加拿大和墨西哥)次之，占全球GDP的23%。高盛(Goldman Sachs)也预测，到2050年，中国将成为世界最大的经济体，紧随其后的是美国和印度。
但中国和印度的崛起并不意味着美国的衰落。付出代价的将是欧洲，它在全球GDP中所占的份额将会下降，主要是由于人口原因。部分预测显示，半个世纪后，整个欧洲的人口将少于美国。如果高盛的预测是正确的，即2050年美国、墨西哥和加拿大占全球GDP的份额为23%，那么美国在全球总量中所占的份额将与70年前，也就是1980年大致相当，当时的份额是22%。而美国的人均收入，至少到22世纪都将大大超过中国和印度，即便不是22世纪以后的话。
事实可能证明，在从1900年到2050年的150年里，美国在全球经济中的相对规模都出奇的稳定。一些新保守派人士在将美国与二战前的英国相比较时，往往会低估美国的实力。尽管存在伊斯兰圣战分子，但当今世界远比30年代安全。不过无论如何，当代美国不应该与1937年的英国相比，而应该与1937年的美国相比，当时的英国拥有全球10.2%的军事力量，美国则拥有全球41.7%的军事力量。
但如果美国全球霸权的支持者因美国在全球力量中所占潜在稳定份额而振奋，那就错了。一个长期可能占世界GDP约四分之一的国家，在今后几代人的时间里，都可以在多极世界的各强国中保持第一，但如果试图成为新罗马帝国，让过度的军事动员削弱了经济实力，那么美国很可能会成为下一个苏联。
作者系新美国基金会(New America Foundation)怀特海(Whitehead)高级研究员
