War in an age of terrorism reveals the limited effectiveness of armed force. Yet the belief that higher military spending buys more national security remains strong. President Trump’s proposal to add $54 billion, or nearly 10 percent, to the Pentagon budget presents the latest example of chasing this false hope.

The president’s request for a huge arms buildup emerges from one of two contradictory impulses he has shown. On one hand, Trump has criticized the Iraq war, talked about avoiding new conflicts and implied that money spent in Iraq and Afghanistan could have been better used for peaceful projects at home.

In his Feb. 28 address to Congress, the president said: “With the $6 trillion, we could have rebuilt our country twice, and maybe even three times.” Fact-checkers called the $6 trillion figure high, both for the cost of the wars since 2001 and as an estimate of infrastructure needs, but the basic point was right: Wars steal resources from productive, peaceful uses. Rarely has a president raised this idea since Dwight D. Eisenhower said in 1953 that “every warship launched, every rocket fired signifies, in the final sense, a theft from those who hunger and are not fed, those who are cold and not clothed.” Trump at least implicitly questioned the value of recent war spending.

On the other hand, the president has repeatedly claimed the U.S. military is in steep decline and needs a massive infusion of funds. While Pentagon budget increases are routine — the Obama administration recommended a 6 percent raise for fiscal 2018 — analysts have observed that Trump’s spending preferences reveal an outdated view of military power.

New York Times writer Max Fisher has noted Trump’s desire to build up major weapons systems, such as aircraft carriers and nuclear weapons, fits the mindset of 20th-century great-power wars more than the unconventional wars the U.S. is fighting today. Fisher believes Trump is fascinated with “high-priced assets” without clear purposes and may see the weapons as “stagecraft,” or ends in themselves. Further, Trump has complained the U.S. no longer wins wars. But he may find, as his predecessors did, that fighting terrorists doesn’t produce classic battlefield victories and that a “war on terror” may be unwinnable in a traditional sense.

The president will hear a realistic view of the limits of military force if he listens to knowledgeable advisers. These include retired military officers who wrote a letter to congressional leaders warning against cutting the State Department and foreign aid budgets. These military leaders stressed the importance of diplomacy and development aid — the “soft power” tools that prevent conflict. “The crises our nation faces do not have military solutions alone,” the retired officers said. The “drivers of extremism” include “lack of opportunity, insecurity, injustice and hopelessness.”

Force alone doesn’t achieve peace, these military people are saying. Soft power is essential for global stability. But bad policies undercut its positive impact. An attempted travel ban impacting Muslims fuels the perception of Western hostility toward Islam. A drastic reduction in the State Department Food for Peace Program, which Trump’s budget proposes, would damage humanitarian efforts that prevent or ease conflict.

Analysts predict the president won’t get the 10 percent military spending increase he is seeking. We hope that is true. We also hope he will show more flashes of his good instincts. In 2013 Trump said he favored a full withdrawal from Afghan­­istan, where the longest conflict in American history has cost three-quarters of a trillion dollars and the lives of nearly 2,400 U.S. soldiers. But last year he said Americans would keep fighting there, although “I hate doing it so much.” Hold on to that thought, Mr. President.