The growing risk of a superpower's self-justified actions destabilizing the global economy and afflicting people's lives is deeply concerning.

When former U.S. President Donald Trump won reelection, stock prices in both Japan and the United States surged. Trump has promised to substantially cut corporate taxes and to ease regulations, a move seen as stimulating the economy. Market reactions, however, may have come too soon. Trump, waving an "America First" banner, is seeking to escalate protectionist policies that excessively prioritize his own country.

Eyeing 60% tariffs on goods from China

Trump's weapon of choice is tariffs, calling it "the most beautiful word in the dictionary." The president-elect announced his plans to impose tariffs of 10-20% on goods from all countries, including Japan and other allies in Europe. For China, a country he regards as a threat, he plans a 60% tariff. This is much higher than the tariffs of up to 25% levied on goods from China during Trump's first term.

If implemented, the average rate of American tariffs will surge from around 3% to 17%. This would be the highest level since the 1930s, when the world was hit by the Great Depression. At the time, countries imposed high tariffs on each other in an attempt to shut out imports from other nations. This deepened conflicts that eventually triggered World War II.

The greatest concern is the possibility of a trade war between major powers.

During Trump's first term, both China and Europe hit back, and an exchange of high tariffs unfolded. The economic outlook became uncertain, and stock prices fell globally. This time, Trump appears to have stepped up his hardline approach, and a retaliatory battle could intensify. International supply chains could be cut, and trade could fall greatly. The repercussions for the world would be massive.

The International Monetary Fund predicts that global economic growth could deteriorate far below the 3% threshold said to divide good economic conditions from bad. The fund's Managing Director Kristalina Georgieva has warned that prolonged low growth could increase poverty in developing nations and inequality could spread.

There is also a risk that inflation in the U.S. could flare up again, because if high tariffs are imposed, it would push up the price of imports.

The U.S. has just gotten over a historically high period of inflation and the Federal Reserve Board has pivoted to a stance of cutting interest rates to support the economy. But if prices rise again, then it could be forced to raise interest rates once more. If U.S. interest rates rise and investors buy the dollar, currencies other than the dollar, including the yen, will weaken, spreading price hikes across the globe. And this would hit people on low incomes the hardest.

The multilateral framework that has supported the global economy would also likely be shaken.

Summits of the Group of Seven major industrial countries and the Group of 20 industrialized and emerging-market nations have served as forums for aligning policies on trade and other issues. Trump, however, has historically made light of international cooperation, clashing with other countries at those summits. That is because he cannot use the same methods he uses in bilateral negotiations, extracting favorable terms by intimidating the other country with the hint of high tariffs, backed by the United States' economic and military strength.

Fissures in the international community over the wars in Ukraine and the Middle East are growing deeper. There are many risks to the global economy, and to achieve stability, it is essential for each country to collaborate. As a superpower, the U.S. is in a position to lead negotiations. It would be irresponsible to neglect that role and escalate divisions.

Self-justification threatens US interests

Trump's victory is attributed to his wins in key battleground states with a high concentration of automobile, steel and other factories supporting the U.S. economy. Many of these areas have receded, to become part of the "Rust Belt" of industrial decline after being held back by cheap imports from China, among other factors.

During the presidential election, Trump stressed that many jobs were being taken by China and other countries, and that he would get them back, and appealed to laborers on low incomes with his high tariff policy. But in spite of high tariffs on steel products from China, Japan and other countries, U.S. Steel Corp. was unable to emerge from decline, and the company agreed to sell itself to Nippon Steel Corp. This happened because its high-cost structure was protected by tariffs. Trump is opposed to the sale, but he needs to recognize there were flaws in his approach.

The U.S. economy has developed because it has helped promote free trade and investment throughout the world, inspired by reflection on prewar protectionism. Self-righteous policies will not open up new opportunities for the future.

Protectionism undermines the United States' national interests. Japanese Prime Minister Shigeru Ishiba and other leaders should explain to Trump the significance of open markets and urge him to review his trade policies.