(Bloomberg) -- Chubb Ltd. Chief Executive Officer Evan Greenberg said the U.S. must avoid the risk of becoming so inward-looking that the nation cedes its historic role in shaping a liberal order that has benefited the country for decades.

“Without U.S. leadership, the system lacks confidence and our allies and others seek alternatives,” Greenberg wrote in his annual letter, which was published on the company’s website. “If we don’t defend this world order, and if we allow our current populism to turn into protectionism and simply follow a narrow view of an America First policy, other countries will naturally follow suit with their own brand of nationalism.”

'Cautiously optimistic'

Greenberg didn’t mention President Donald Trump by name in the letter. While the CEO said he’s "cautiously optimistic" about many of the administration’s economic policies, "particularly around deregulation for business, tax reform, and infrastructure and military spending," the CEO stressed the importance of close ties with Mexico, a nation where he has expanded through acquisitions. And Greenberg criticized Russia’s Vladimir Putin, a leader who has won praise until recently from Trump.

“A stable, growing, prosperous and open Mexico, friendly to the U.S., is in our national interest,” Greenberg wrote. “Russia is not our friend and no one should misunderstand them. Russia and Putin want to reassert their influence — they do not respect nation-state borders, physical or cyber, and they have a desire to undermine democratic states.”

‘Set the tone’

Greenberg, 62, built one of the world’s largest insurers last year by combining his Ace Ltd. with Chubb Corp. The Zurich-based company operates in more than 50 nations. He has been vocal on the benefits of globalization, saying in February that the U.S. needs to remain open to people from the rest of the world. Those remarks followed an order by Trump to limit travel to the U.S. from some Muslim-majority countries. The letter built on Greenberg’s warnings.