David Chou and Pastor Billy Chang spent their whole lives forging parallel paths. They were born in early 1950s Taiwan, grew up just miles apart during martial law and later rebuilt their lives in the United States.

But over several decades, they carried with them vastly different memories — and views — of the island of their birth.

Mr. Chou was the son of parents who fled mainland China following the 1949 Communist revolution, part of a mass exodus of Chinese who established an authoritarian government-in-exile in Taiwan. Though he was born on the island, he and his parents were “mainlanders” devoted to the Chinese motherland and saw Taiwan as forever part of China.

Pastor Chang’s relatives were local Taiwanese who had spent centuries on the island. At home, he spoke Taiwanese Hokkien, a language that for decades was banned in public spaces. Pastor Chang grew to believe that despite Beijing’s longstanding claims, the self-ruled island had its own identity, separate from China.

In May, the lives of the two men collided in a quiet retirement community in Southern California. Authorities say that Mr. Chou, 68 — armed with two guns, four Molotov cocktails and a deep-seated rage against Taiwanese people — opened fire inside the Irvine Taiwanese Presbyterian Church as members gathered in honor of Pastor Chang, 67.

The mass shooting was part of a spate of violence that has stunned the nation in recent weeks. One day before, a white 18-year-old fueled by racist hate killed 10 Black people at a Buffalo grocery store. Less than two weeks later, an 18-year-old massacred 19 students and two teachers at an elementary school in Uvalde, Texas.

But the shooting in the church in Laguna Woods, Calif., stood out in its own way, a variation on American tragedy that seemed to show how faraway conflicts, even those in the distant past, can reverberate in the gun culture of the United States.

At the Southern California church, a crowded May 15 lunch celebration for Pastor Chang gave way to an eruption of gunfire. Mr. Chou fatally shot a doctor, John Cheng, 52, who tried to stop him, police said. Pastor Chang then threw a chair at the gunman, allowing others to subdue and tie him up with an extension cord. Five congregants, ranging in age from 66 to 92, were injured.

Mr. Chou is being held without bail on charges of murder and attempted murder pending an August arraignment.

As with internal tensions over the years in immigrant communities worldwide — California’s Little Saigon and Miami’s Cuban-American precincts are two U.S. examples — the crime has echoed across the Taiwanese diaspora and underscored divisions that remain frozen in time, even as younger generations have moved beyond them.

“How do we reconcile the views of these identities?” said Annie Wang, 42, a Northern California-based co-host of the podcast “Hearts in Taiwan,” noting that her parents spent years avoiding talk of the schisms related to Taiwanese independence. “It’s been so behind closed doors, but I can’t see a way around this anymore. Someone went and killed for this.”

The shooting has also deepened fears about safety in a time of rising anti-Asian attacks in the United States and underscored debates about access to firearms and mental health services. Those who know Mr. Chou say he had been unraveling for years and was desperate in the face of eviction, a dying wife and financial troubles.

A Strong Taiwanese Identity

Growing up in the countryside of central Taiwan in the 1960s, Pastor Chang always felt at home at church. His father was a Presbyterian pastor, and the congregation members, mostly local Taiwanese farmers, would often bring the young family selections of their latest harvests: water spinach, cabbage and rice.

Outside of that community, Pastor Chang was not always shown such favor. He was a benshengren, a descendant of long-ago ethnic Chinese settlers. His classmates whose families had just fled the mainland, or waishengren, enjoyed certain advantages he did not have.

Under the authoritarian rule of Chiang Kai-shek’s Nationalists, who lost the civil war to the Communists, mainlander families received preference for civil servant jobs and government positions. Schools were required to teach in Mandarin and promote a Chinese identity, while Taiwanese Hokkien was forbidden in public spaces. Over four decades, tens of thousands of people who dissented from the government’s policies were arrested, and at least 1,000 — more than half benshengren — were executed.

Pastor Chang said he went through a “late political awakening” in the 1980s while in seminary, devouring forbidden texts that discussed this political repression and pushed the idea of a distinct Taiwanese identity. He joined large protests to call for freedom of speech, the first buds of a movement that would eventually lead to democracy in Taiwan in the 1990s.

Pastor Chang emigrated to the United States in 1991 following his parents and siblings, assured in his own Taiwanese identity. He led a small church in Camarillo, Calif., before joining Irvine Presbyterian in 1999. Over time, the congregation grew beyond 150 people and became the largest of about 40 official Taiwanese Presbyterian congregations in the United States.

Immigrants from Taiwan joined waves of Chinese-speaking immigrants from mainland China and Hong Kong, and they included both benshengren and waishengren. By and large, they have all coexisted peacefully in their adopted country, and tensions over homeland politics have rarely risen to the surface.

In the United States, Taiwanese Presbyterian churches have become a social hub for older congregants to bond over their common language and shared experiences. At church bazaars, grandmothers and aunties cook beloved Taiwanese snacks, including sticky rice wrapped in bamboo leaves, and oyster pancakes.

“That’s what I remember church being: celebration and remembrance of your culture,” said Peggy Huang, 51, a Yorba Linda city councilwoman whose parents are members of the Laguna Woods church.

While the church was not overtly political, the belief in a separate Taiwanese identity suffused the institution. Unlike some Taiwanese-led churches that offer services in Mandarin or English, most Taiwanese Presbyterian churches in the United States adhere to the Taiwanese language. Pastor Chang said it stemmed partly from their view of Mandarin as the “language of the oppressors.”

In addition to lectures on topics like combating dementia and estate planning, the Laguna Woods church has organized talks on the 2/28 Incident, during which the Nationalist government killed up to 28,000 people in Taiwan in the late 1940s. During services, members often pray for Taiwan’s safety in the face of China’s rising threats. Pastor Chang said his congregation had very little interaction with the waishengren in Laguna Woods, who mostly attend a Mandarin-language church.

“It would be an overstatement to call us a pro-independence church,” Pastor Chang said. “But we do not deny that we love Taiwan.”

Love for the Motherland

Mr. Chou grew up with the trappings of a middle-class life: He lived with his four siblings in a modest, two-story concrete house in the central city of Taichung. Because his father was an officer in the Nationalist army, his family was treated favorably and he attended one of the top high schools on the island.

But the waishengren community was also steeped in the pain of having to flee mainland China when Communists took over. And Mr. Chou decades later told friends he was bullied and hit by the children of longtime Taiwanese families. (The divide between the two communities still shapes politics in Taiwan, but political violence is rare.)

Friends and relatives of Mr. Chou have been trying to make sense of the mass shooting. But those familiar with his political leanings were less surprised.

“Of course, we feel bad for the victims, but he did it for a reason,” said James Tsai, a friend of Mr. Chou’s in Las Vegas, pointing to resentment fueled by the childhood bullying.

Like many waishengren of his generation, Mr. Chou held on to a romanticized vision of China as a lost homeland even after he moved in 1980 to the United States, where he worked in the hospitality industry.

In the preface to a mixology book published in 1994, Mr. Chou called Mao Zedong and Deng Xiaoping “great leaders” for making China prosperous. He resented the emergence in Taiwan in recent decades of a Taiwanese identity separate from China and rooted in the island’s democratic values. In a 2018 book, Mr. Chou called benshengren “poisoned” rebels who had betrayed their Chinese ancestors with their pro-independence views.

Mr. Chou settled down in Las Vegas, where he and his wife bought property that they rented out to help put their two sons through dentistry school. But Mr. Chou soured on the United States in 2012 after he was assaulted by a tenant over a rent dispute, according to friends and his 2018 book. The attack fueled what would become an obsession with guns.

Several members of the local Taiwanese Presbyterian Church and a Taiwanese social club said Mr. Chou mingled occasionally with the benshengren community at their events. Most were unaware of his political views until 2019, when his photo appeared in an article about an event hosted by a pro-China group.

“Swiftly eliminate the monsters of Taiwanese independence,” read a banner that Mr. Chou brought to the event.

In a telephone interview, Jenny Koo, chairwoman of the organization, said she had met Mr. Chou only twice and that she remembered thinking his political views were “too radical.”

It remains unclear why Mr. Chou targeted the church in Laguna Woods. He has a brother who lives in the area, according to friends and his niece.

The police said last month that the gunman acted alone when he chained, nailed and super-glued shut the doors to a multipurpose room before he opened fire on congregants. Several days later, the Los Angeles office of the World Journal, a Chinese-language newspaper, said that it had received seven handwritten journals titled “Diary of an Independence-Destroying Angel” from Mr. Chou.

On Friday, Mr. Chou stood at the front of a cage, making fleeting eye contact with attendees at a hearing in a Santa Ana, Calif., courtroom. He wore a blue surgical mask and a lime green jumpsuit used for inmates in protective custody.

The Ripples of History

The Laguna Woods shooting came as a shock to many in the Taiwanese and Chinese diaspora, particularly those in the younger generation who grew up in the United States and felt little connection to decades-old grievances.

Ms. Wang, the podcast co-host, said that as a child, she struggled to understand why her mother identified as a Chinese American, even though she spoke Taiwanese and her family had been in Taiwan for generations.

It was not until Ms. Wang, and a cousin, Angela Yu, began learning more about Taiwan’s history that they understood the fraught nature of identity in the diaspora, and why their parents adhered to their Chinese American identity while friends’ parents emphasized being Taiwanese.

The cousins, who now identify as both Chinese American and Taiwanese American, started their podcast to discuss these thorny issues.

“The time that our parents immigrated was a freezing of identity, and they passed those ideas about identity on to their kids,” Ms. Wang said.

She added that she hoped the shooting would open the door for the diaspora to “speak more openly and honestly” about these struggles.

Reflecting on the church confrontation, Pastor Chang sounded a note of resignation.

“The gunman and I, our generation, had the misfortune of being born during a political era that forced our two groups to not get along,” he said. “That is the original sin of our generation.”

Amy Qin reported from Taipei, Taiwan. Jill Cowan reported from Laguna Woods, Calif. and Santa Ana, Calif. Shawn Hubler reported from Sacramento. Amy Chang Chienreported from Taichung, Taiwan.