以史为鉴，特朗普的贸易关税恐让美国重演大萧条

前几天，美国总统唐纳德·特朗普震惊了世界。他冲动地宣布将对进口钢铁和铝产品征收高关税，全球股市随即大跌。此前特朗普还威胁要对欧洲出口美国的汽车征税。

股市的反应和经济学家一样，都不喜欢关税。关税会妨害市场基本运行效率，除了保住少许就业岗位几乎没什么正面意义，却会导致经济价格整体上涨。有个少有人知的例子可以说明关税的作用，就是导致美国经济大萧条的《斯姆特-霍利关税法》（Smoot-Hawley Tariff Act）。

当然，大萧条的原因现在还颇有争议。常见的一种看法是，1929年美股崩盘导致了大萧条。但更了解情况的人会说，根本原因是美联储过度宽松的信贷政策和错误收紧货币政策。《斯姆特-霍利关税法》直到1930年6月17日才得到总统签署成为立法，当时股市已从1929年高位跌落，所以通常被视为酿成大萧条的次要因素。

但更仔细研究一下就会发现，上述时间线有误导性。智库卡托研究所转载了美国杂志《国家评论》（National Review）1979年发布的大萧条成因分析文章，其作者艾伦·雷诺兹认为，《斯姆特-霍利关税法》曾持续拖累美国经济。不仅如此，他还认为该法案对1929年股市崩盘负有很大责任，因为交易者已预知该法案出台。

雷诺兹的观点很有道理。据此猜测，特朗普可能推出的关税政策结果相当可怕。

雷诺兹指出，美国众议院1929年5月通过了《斯姆特-霍利关税法》，此后法案每通过一道立法流程，股市就震荡一次。同年10月23日星期三的市场显示，关税政策影响范围远超最初预期。

第二天就是证券史上著名的黑色星期四，当天大跌9%，持续数年的暴跌也由此拉开帷幕。

雷诺兹总结道：“市场参与者不是重大法案正式通过之后”才开始抛售，1929年就开始调低仓位。最终，《斯姆特-霍利关税法》上调了数以万计进口产品的关税。贸易政策分析师比尔·克里斯特指出，到1934年年末，全球贸易规模较1929年缩水了66%。

现在的情形和当年一样令人不安。特朗普的关税政策还未生效，目前正式决定征收关税的商品只有钢铁和铝。但未来几天，股票交易者会根据对未来发展形势的判断行动。有些迹象跟1929年类似，起初关税影响范围有限但很可能扩大。美国的贸易伙伴已经纷纷表示，若关税生效必将采取报复手段。特朗普却宣称：“贸易战是好事。”

即便人们认同雷诺兹等人的看法，关税也只是导致当年大萧条的因素之一，其他原因大多未经证实。但说到关税的实际影响，历史上已有非常值得警惕的教训，股市也很可能应声而动。（财富中文网）

译者：Pessy

审稿：夏林

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.