Marc Kornblatt prepared uneasily last month for his daughter, Louisa, to arrive for 10 days with the family. Her homecomings once brought the comfort of movie nights and card games, but this year was different.

Mr. Kornblatt sang under his breath some lyrics from “West Side Story”: “Get cool, boy.” He and his wife discussed: How would they greet their child? Would they acknowledge the emotional distance, the slights that had piled up from afar?

He and his wife, Judith, had moved away from Madison, Wis., to live in Tel Aviv, where they felt a real sense of belonging as Jews. Around the same time, their daughter, attending graduate school at the University of California, Berkeley, came to oppose the existence of Israel as a Jewish state.

The political divide between two generations within the family has grown into a painful chasm during the war between Israel and Hamas. Until late November, it was addressed mostly in tense exchanges on WhatsApp. “Really sad that you seem out of touch with where our heads are at,” Mr. Kornblatt had messaged his daughter after she told her parents about a friend speaking out in support of people in Gaza.

As she packed her bags to go to Tel Aviv, his daughter questioned how her parents could argue about a political solution that felt morally urgent to her: a permanent cease-fire.

“It feels so simple — just don’t murder people. Don’t kill people. Just stop it,” said Louisa Kornblatt, 31, who now lives in Brooklyn. “It feels so simple, and a lot of my mom’s responses are like, ‘It’s so complex.’”