As Violence Surges, Nations Seek U.S. Defense Pacts. Some Americans Are Wary.

From around the world, they come to the halls of power in Washington seeking one thing: a commitment from the American government to protect their countries in a time of rising geopolitical crises.

In recent months, leaders and diplomats from a growing number of nations have signed security pacts with the United States, upgraded military ties and weapons purchases or have begun negotiating potential new defense treaties and arrangements.

The countries include Ukraine, at war with Russia; Saudi Arabia and Bahrain, eager to stave off Iran; and Japan, South Korea, Australia and the Philippines, anxious about China and North Korea’s military ambitions. Frightened by Russia’s aggression, Finland joined the North Atlantic Treaty Organization in April, while Sweden is on the brink of membership.

The Biden administration is surging munitions to Israel for airstrikes in Gaza and has sent two aircraft carrier groups to the eastern Mediterranean. Israel and the United States have a series of agreements on military aid.

The push around the world for the United States to be all things to all partners in terms of defense is stronger than at any time since the end of the Cold War. But many Americans are resisting having their nation play that role, at least partly because of the political impact of the disastrous U.S. wars in Iraq and Afghanistan.

And critics say the devastating attacks by Hamas on Oct. 7 that killed about 1,400 Israelis underscore the fact that defense agreements do not create a real foundation for peace and deterrence.

That opposition to the United States being what President Biden and other U.S. officials call “the indispensable nation” — they mean the security guarantor around the world — has some roots in traditional liberal antiwar values, but it is also tied to surprising ideological shifts of recent years. Many Republican voters, once proponents of a Cold War and antiterrorism global military footprint, now support isolationist and pro-Russia politicians, notably former President Donald J. Trump.

Some Republican lawmakers are now trying to halt aid to Ukraine, and progressive Democrats have denounced the ongoing Israeli airstrikes that have killed thousands of Palestinians. All of that sets up a potential battle over a new White House request for $105 billion of military aid that would go mostly to Ukraine and Israel.

Democratic senators have also raised doubts about the Biden administration’s efforts to negotiate a defense treaty with autocratic Saudi Arabia that would resemble the agreements the United States has with Japan and South Korea, decades-long democratic allies.

Despite the signs of American opposition, countries across Europe, the Middle East and Asia still consider the United States the most — and perhaps the only — viable guarantor of their security. And U.S. officials say the alliances remain a pillar of what they call the “rules-based international order.”

Mr. Biden has reinforced that notion, most recently in a speech on Oct. 19 in which he made the case for military aid to Ukraine and Israel.

“American leadership is what holds the world together,” he said. “American alliances are what keep us, America, safe. American values are what make us a partner that other nations want to work with. To put all that at risk if we walk away from Ukraine, if we turn our backs on Israel, it’s just not worth it.”

But some lawmakers and analysts say other countries, including wealthy European nations fearful of Russia, need to take greater responsibility for their defenses.

“U.S. allies and partners are concerned about U.S. overstretch,” said Stephen Wertheim, a historian of American foreign policy and senior fellow at the Carnegie Endowment for International Peace. “But paradoxically, if they have put enough chips to date in the U.S. basket” of military ties, he added, “they want to seek closer relationships and more formal commitments from the United States.”

“From the perspective of the U.S.,” he said, “although there is great recognition in Washington that the unipolar moment is over, there’s still a reliance on U.S. security umbrellas along the lines of, ‘We know how to provide for peace and stability.’ There’s a presumption that the U.S. security umbrella is the solution.”

Defense agreements between the United States and other nations come in all shapes and sizes. The strongest, which usually need approval by two-thirds of the Senate, guarantee mutual defense if one country is attacked. Article 5 of the NATO charter is a prominent example.

Some agreements, such as the new one with Bahrain, are a step down, requiring only that the countries consult with each other in the event of hostilities. Israel is not one of the 52 treaty allies of the United States, but some Israeli officials have discussed whether to push for a formal pact.

After the attacks of Sept. 11, 2001, the United States and its partners became more concerned about nonstate adversaries like Al Qaeda, and they focused their energies on the so-called global war on terror. But in recent years, as Russia and China have acted with greater military aggression, and as Iran and North Korea have advanced their nuclear and missile programs, many countries have sought to upgrade their ties with the United States.

The strategies in this era of so-called great-power competition hark back to the alliance and bloc building that took place during the Cold War.

Security umbrellas can sometimes deter adversaries from attacking. President Vladimir V. Putin of Russia has refrained from strikes on any NATO nation even though those countries support Ukraine’s military. But the pacts can also appear flimsy: China’s naval and coast guard vessels act aggressively toward the ships of countries that are U.S. treaty allies — even ramming two Philippine military vessels on Sunday.

The most controversial move by Mr. Biden to forge a new mutual defense treaty involves Saudi Arabia. The kingdom is by far the biggest buyer of American weapons, and the U.S. military helps train its forces. But Crown Prince Mohammed bin Salman wants much more. He has pressed the Biden administration for a Senate-ratified defense treaty that would commit the United States to protecting Saudi Arabia if it is attacked.

The treaty is Prince Mohammed’s biggest demand as a condition for normalizing ties with Israel, though the Saudis are in wait-and-see mode on the normalization talks as the Israel-Hamas war unfolds.

The prince has made an implicit threat that Saudi Arabia could move its main security relationship, including arms purchases, to another country, likely China, if it does not get a treaty with the United States. But some analysts say he is bluffing: The Saudi military is built around American weapons, and China’s military currently cannot project force in the Middle East and prefers to avoid becoming entangled in conflicts there. Without a treaty, the United States maintains more leverage over Saudi Arabia, they say, even as the kingdom grows its diplomatic and economic ties to China.

“The idea that a U.S. security guarantee will somehow peel Saudi Arabia away from China is naïve in the extreme,” Emma Ashford, a senior fellow on U.S. foreign policy at the Stimson Center, wrote this month. “Indeed, the most likely scenario for this deal is that the U.S. will take responsibility for Saudi security while China remains the kingdom’s most important economic partner. This seems like a poor trade.”

Since the Hamas attacks, other analysts have said that efforts by the Trump and Biden administrations to sell advanced weapons to Arab autocrats in exchange for those leaders normalizing ties with Israel in the Abraham Accords did nothing to expand options for peace in the Israeli-Palestinian conflict. In fact, they say those efforts helped increase tensions among Palestinians, who believe their aspirations for nationhood are being buried.

“The Biden doctrine presumed that the Palestinians could be shunted aside and offered some crumbs to keep them quiet,” Matt Duss, an advocate of progressive foreign policy, wrote in Foreign Policy. “No attempt would be made to address a key source of violence: the Israeli occupation of the West Bank, Gaza and East Jerusalem, now more than half a century old.”

Mr. Biden faces resistance from his own party on a U.S.-Saudi defense treaty. On Oct. 4, a group of Democratic senators sent a letter to the president asking whether U.S. interests would be undermined by such a treaty, given Prince Mohammed’s dismal record on human rights, including his war in Yemen.

Defending Ukraine is also an increasingly thorny issue for Mr. Biden, but here it is Republicans who are balking. Republican lawmakers cut funding for Ukraine from stopgap government spending legislation passed last month. Now Mr. Biden is fighting to get Ukraine funding approved by Congress.

And Ukraine wants more. President Volodymyr Zelensky has pushed for his country to enter NATO. Barring that, he has said the United States and Europe must come up with a new “security architecture” to address Russia’s persistent threat.

The Reagan-era Republican Party might have jumped at a chance to support Ukraine, but Mr. Trump admires Mr. Putin and is pulling Republicans into the pro-Russia camp.

If Mr. Trump were to become president again, he would not only likely cut off aid to Ukraine, but he also might withdraw the United States from NATO and scrap the alliances with Japan and South Korea.

The traditional American security role in the world would end, an epochal change that would bring relief to some — but distress to others.

“A Trump victory would be a systemic shock for Europe,” said Constanze Stelzenmüller, director of the Center on the United States and Europe at the Brookings Institution. “Policymakers and politicians are frantically debating hedging strategies, but there is no credible full replacement for the U.S. security umbrella.”