以史為鑒，特朗普的貿易關稅恐讓美國重演大蕭條

前幾天，美國總統唐納德·特朗普震驚了世界。他沖動地宣布將對進口鋼鐵和鋁產品征收高關稅，全球股市隨即大跌。此前特朗普還威脅要對歐洲出口美國的汽車征稅。

股市的反應和經濟學家一樣，都不喜歡關稅。關稅會妨害市場基本運行效率，除了保住少許就業崗位幾乎沒什么正面意義，卻會導致經濟價格整體上漲。有個少有人知的例子可以說明關稅的作用，就是導致美國經濟大蕭條的《斯姆特-霍利關稅法》（Smoot-Hawley Tariff Act）。

當然，大蕭條的原因現在還頗有爭議。常見的一種看法是，1929年美股崩盤導致了大蕭條。但更了解情況的人會說，根本原因是美聯儲過度寬松的信貸政策和錯誤收緊貨幣政策。《斯姆特-霍利關稅法》直到1930年6月17日才得到總統簽署成為立法，當時股市已從1929年高位跌落，所以通常被視為釀成大蕭條的次要因素。

但更仔細研究一下就會發現，上述時間線有誤導性。智庫卡托研究所轉載了美國雜志《國家評論》（National Review）1979年發布的大蕭條成因分析文章，其作者艾倫·雷諾茲認為，《斯姆特-霍利關稅法》曾持續拖累美國經濟。不僅如此，他還認為該法案對1929年股市崩盤負有很大責任，因為交易者已預知該法案出臺。

雷諾茲的觀點很有道理。據此猜測，特朗普可能推出的關稅政策結果相當可怕。

雷諾茲指出，美國眾議院1929年5月通過了《斯姆特-霍利關稅法》，此后法案每通過一道立法流程，股市就震蕩一次。同年10月23日星期三的市場顯示，關稅政策影響范圍遠超最初預期。

第二天就是證券史上著名的黑色星期四，當天大跌9%，持續數年的暴跌也由此拉開帷幕。

雷諾茲總結道：“市場參與者不是重大法案正式通過之后”才開始拋售，1929年就開始調低倉位。最終，《斯姆特-霍利關稅法》上調了數以萬計進口產品的關稅。貿易政策分析師比爾·克里斯特指出，到1934年年末，全球貿易規模較1929年縮水了66%。

現在的情形和當年一樣令人不安。特朗普的關稅政策還未生效，目前正式決定征收關稅的商品只有鋼鐵和鋁。但未來幾天，股票交易者會根據對未來發展形勢的判斷行動。有些跡象跟1929年類似，起初關稅影響范圍有限但很可能擴大。美國的貿易伙伴已經紛紛表示，若關稅生效必將采取報復手段。特朗普卻宣稱：“貿易戰是好事。”

即便人們認同雷諾茲等人的看法，關稅也只是導致當年大蕭條的因素之一，其他原因大多未經證實。但說到關稅的實際影響，歷史上已有非常值得警惕的教訓，股市也很可能應聲而動。（財富中文網）

譯者：Pessy

審稿：夏林

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Donald Trump stunned the world last Thursday with his reportedly impulsive announcement of steep U.S. tariffs on steel and aluminum. Stock markets responded by dropping sharply around the world — and that was before Trump doubled down by threatening to impose tariffs on European cars.

Both stock markets and economists tend to loathe tariffs, which hamper the basic efficiency of the market, rarely accomplishing more than saving a few jobs in exchange for higher prices across the entire economy. One illustration of this that’s not as widely known as it should be is the role of tariffs, specifically a set of rules known as the Smoot-Hawley Tariff Act, in triggering the Great Depression.

Obviously, the causes of the Depression are still hotly debated, and popular understanding centers on the 1929 stock market crash, while the somewhat more informed will cite excessive easy credit and misguided tight monetary policies by the Federal Reserve. Smoot-Hawley wasn’t signed into law until June 17, 1930, when stocks had already plunged from 1929 peaks, so it’s often seen as a secondary factor.

But a closer look shows that timeline is misleading. In a 1979 National Review analysis of the causes of the Depression reprinted by the Cato Institute, author Alan Reynolds argued that Smoot-Hawley was an ongoing drag on the economy. More than that, though, he thought it substantially contributed to the stock market collapse of 1929, because traders saw it coming.

His argument is compelling — and, as an indicator of the possible fallout of the Trump tariffs, scary.

Smoot-Hawley, Reynolds points out, passed the House in May 1929, and stocks were battered every time the act moved through the legislative process. On Oct. 23 of that year, a Wednesday, it became clear the tariffs would be much broader than first believed.

The very next day, of course, was Black Thursday. Markets dropped 9% in a day and kicked off a yearslong stock meltdown.

As Reynolds sums up, “market participants do not wait for a major law to pass” before retrenching their positions. In 1929, they were right to sell. Smoot-Hawley ultimately raised tariffs on tens of thousands of products, and trade policy analyst Bill Krist points out that by the end of 1934, global trade had tanked by 66% from 1929 levels.

The parallels to the current moment are distressing. The Trump tariffs are not in effect yet, and so far they are officially limited to steel and aluminum. But in coming days, stock traders will be acting on their beliefs about what the future will bring. There are signals, just as there were in 1929, that tariffs could expand from their modest start — U.S. trade partners have already said they will retaliate if tariffs go into effect, while President Trump posits that “trade wars are good.”

Even if we accept arguments like Reynolds’, tariffs were just one factor in the Depression, and most of the others aren’t substantial now. But history has provided us with a strong cautionary lesson about the real impact of tariffs, and the stock market is likely to heed it.