Beijing has picked off Taiwan’s remaining allies. Taiwan is fighting back.

Taiwan President Lai Ching-te has been traveling across the region this week to shore up support from those countries—three of Taipei’s dozen remaining official allies—while stopping in Taiwan’s biggest, albeit unofficial, ally, the U.S.

On Thursday, the Taiwanese president arrived in Palau, the final stop of his first overseas trip since taking office this year. Lai’s seven-day long trip saw him making stops in the three Pacific nations with which Taiwan maintains formal diplomatic ties—the Marshall Islands and Tuvalu, in addition to Palau.

The Pacific is a crucial diplomatic front for Taiwan, where it is hoping to prevent Beijing from poaching more of its diplomatic allies. The tiny island nations, analysts say, could also play a strategic role in a potential Taiwan conflict involving the U.S. and China.

If China managed to gain dominance over the Pacific, that would impede U.S. forces from reaching Taiwan for support in a conflict and “become a stronghold for China to attack the United States," said Chang Jung-ming, a research fellow at Institute for National Defense and Security Research, a Taipei-based think tank backed by Taiwan’s military.

China’s Communist Party has never ruled Taiwan but considers the island part of its territory and has vowed to eventually bring it under its control—by force if necessary. Before Lai’s trip began, China’s military vowed to “resolutely crush any ‘Taiwan independence’ separatists," a label that China has applied to the Taiwanese president. Taiwanese security officials also warned of China possibly conducting military drills after his return.

Notably, Lai’s trip included stopovers in Hawaii and the U.S. territory of Guam. Those two transits, which come during a presidential transition in Washington, have prompted protests from Beijing, which opposes any links between Washington and Taipei.

On Thursday, Lai—during a brief stopover in Guam—held phone and video calls with members of Congress, including House Speaker Mike Johnson (R., La.), House Minority Leader Hakeem Jeffries (D., NY) and Sen. Roger Wicker (R., Miss.), the highest-ranking Republican on the Senate Armed Services Committee.

During their phone call, Johnson reassured Lai that supporting Taiwan, and facing up to challenges from China, has bipartisan support on Capitol Hill, according to Karen Kuo, Lai’s spokeswoman.

China has been working hard to woo Taiwan’s remaining official allies, seeking to undermine the island’s international prestige and limit its room to maneuver.

“That kind of trend is alarming, certainly for Taiwan and also for the United States," said Eric Harwit, an Asian studies professor at the University of Hawaii and adjunct senior fellow at the Honolulu-based East-West Center think tank. “We see China using their economic power to win over those island states and also potentially expand their military influence in the region."

Nauru, a tiny Pacific island nation of 12,000 people, severed its relationship with Taiwan in January, just as Taiwanese voters elected Lai. Two months later, Nauru’s president traveled to Beijing to meet with Chinese leader Xi Jinping. In 2019, the Solomon Islands and Kiribati, two nations in the Pacific, broke off their respective ties with Taipei within a week of one another.

Caught in the crossfire is Palau, a nation of roughly 18,000 people and more than 500 islands, a prime target in Beijing’s quest to isolate Taiwan. Palau’s location in the so-called second-island chain, which extends south from Japan through Guam to New Guinea, makes it a potential chokepoint in any regional conflict.

While in Palau, Lai delivered a speech at its legislature and plans to open a government building complex that Taiwan helped to build. On Friday, Taiwan and Palau are set to conduct a joint maritime rescue drill, with Taiwan’s coast guard sending one of its newest domestically-made vessels from its southern port of Kaohsiung, in a possible rehearsal for showdowns with Chinese coast guard vessels in disputed regional waters.

Palau, the site of fierce combat between the U.S. and Japan during World War II, was administered by the U.S. after the war and gained independence in 1994. Along with the Marshall Islands and the Federated States of Micronesia, Palau has a wide-ranging arrangement with the U.S. known as a compact. Under such an arrangement, the U.S. provides those countries with a combined $7.1 billion in aid over the next two decades.

As part of the compact, which was renewed this year, the U.S. provides for the islands’ defense. U.S. Marines completed restoration of a World War II-era Japanese airstrip on Palau’s island of Peleliu in June, part of an effort to upgrade airfields across the region for use in a conflict. The U.S. is also building an advanced radar facility on Palau to increase early-warning capacity.

In 2017, with Taiwanese voters having elected a government skeptical of China a year earlier, Beijing began squeezing Taiwan’s remaining diplomatic allies. Beijing blocked Chinese tour companies from arranging group travel to Palau. Tourists from mainland China, who had accounted for about half of all visitors to Palau, plummeted.

The loss of Chinese visitors, followed by the Covid-19 pandemic, led to a painful contraction in the local economy. But Palau has maintained its Taiwan ties. Local officials said they appreciated the support of a like-minded democracy, and sought to build up tourism from Taiwan, South Korea, Japan and the U.S.

Still, pressure from Beijing has continued. Palau was hit by a cyberattack targeting government records in March. Local officials said the attackers were believed to have links to China.

President Surangel Whipps Jr., who was re-elected in November, expressed concerns during the campaign about Chinese efforts to influence the vote. Recently, he has complained about Chinese survey ships operating in Palau’s exclusive economic zone.

For countries weighing a shift in recognition to Beijing, the possibility of aid and investment beckons. After Xi made the first visit by a Chinese leader to Fiji in 2014, China’s aid to the Pacific region soared. While that assistance declined after 2016, it has increased again in recent years, reaching $256 million in 2022, according to research by the Lowy Institute, an Australian think tank.

China has continued to emphasize its appeal to Pacific island nations. Last week, Xi hosted the prime minister of Samoa, one of Beijing’s most longstanding allies in the region. Xi told Prime Minister Fiamē Naomi Mataʻafa that China would “tap the potential of economy, trade, investment, agriculture and fisheries to achieve common development."

To counter China’s efforts, the Taiwanese president has rolled out new offers during his trip in hopes of keeping allies on side.

In the Marshall Islands, Lai attended the opening of an artificial intelligence-powered medical center where Taiwan has helped train surgeons. He also told a banquet that he would boost a scholarship fund.

“We’re both ocean nations, people of the sea, sharing Austronesian culture. We’re one big family, united by our love for democracy and freedom," Lai said.

While in Tuvalu, Taiwanese officials signed a memorandum pledging to help build an undersea cable for the country and underwrite 10 years of operational costs.

Even so, analysts said Taiwan’s approach may not be effective in the long run, since China can offer far more financial assistance.

“The trend is really going against them," said Harwit of the University of Hawaii, referring to Taiwan. “Still, maybe there is enough goodwill from those countries that they don’t, for example, allow China military influence in the region."

Write to Joyu Wang at joyu.wang@wsj.com and Austin Ramzy at austin.ramzy@wsj.com