When visiting synagogues around the world, Jewish tourists from North America are likely to notice one big difference from their home congregations: national flags are rarely inside the sanctuary.

When did this uniquely North American Jewish custom originate, and why? According to Gary P. Zola, executive director of the Jacob Rader Center of the American Jewish Archives and a history professor at the Hebrew Union College-Jewish Institute of Religion in Cincinnati, you can thank a patriotic wave during World War I and, later, the birth of Israel.

About a decade ago, a student asked Zola about the history of flags in American synagogues. That led Zola to a study of the history of the American flag and how it was viewed at different periods. He is currently working on an article summarizing his research.

Though the American flag was officially adopted in 1777, it grew in stature in 1814, the year in which Francis Scott Key wrote what became the national anthem, “The Star-Spangled Banner.” Scott, of course, composed the song after seeing the flag flying defiantly above Fort McHenry after the Battle of Baltimore. The creation of the anthem ignited “the birth of flag culture,” Zola said.

The Civil War was the flag’s “big transformational moment,” he said. At the Battle of Fort Sumter in April of 1861, Confederate forces bombed the fort, causing its main flagpole to fall down. The Fort Sumter Flag became “the martyr symbol of America,” and was shown all around the North and used to raise money for Union war efforts.

Zola said he found evidence of some synagogues displaying American flags inside the sanctuary after Lincoln’s assassination. Still, flags were not a permanent fixture in American synagogues until World War I, with the popularization of the service flag, a banner that used stars to symbolize family members who were fighting or killed in the war.

“These service flags, while they were not literally the American flag, they had a familiarity, they had stars on them and they were American colors,” Zola said. “Churches and synagogues began to fly those service flags inside the sanctuaries as a tribute to the soldiers and as a patriotic symbol.”

This opened the gates to American flags being displayed as a permanent fixture inside synagogues, he said, usually flanking the bimah. Photos from Jewish confirmation ceremonies in the 1920s and 1930s show American flags in the background, and by World War II the practice of displaying flags next to the bimah was “almost ubiquitous,” according to Zola.

Still, for some synagogues the decision to add an American flag was triggered by quite a different event: the emergence of Zionism and creation of the state of Israel. After both the Balfour Declaration in 1917 and Israel’s Declaration of Independence in 1948, synagogues wanted to fly the Zionist or Israeli flags. But many congregants felt that flying a Jewish nationalist flag without an American flag wasn’t right, so they added both.

In most cases, however, the flying of the American flag was not a way for Jews to prove their patriotism, but rather to participate in a defining cultural practice, Zola said.

“American Jews, like in everything else, want to do what Americans are doing. And just as the flag becomes a part of American culture and begins to take on the emotional effect that it has over a period of time, American Jews want to participate,” he said.

Many synagogues didn’t come lightly to the decision to fly a flag. In 1954, Reform leader Rabbi Israel Bettan declared that Old Glory may hang in an American synagogue on the grounds that devotion to the welfare of one’s country “has long assumed the character of a religious duty.” In 1957, Rabbi Moshe Feinstein, the famed Orthodox authority on Halacha, or Jewish law, said secular symbols like flags had no place in the sanctuary; however, since the display of flags does not violate Halacha, a congregation is not required to remove them.

Synagogues tend to follow the etiquette in the U.S. Flag Code, which says the Stars and Stripes should be placed on the leftmost pole, and the other flag to the right (from the audience’s perspective). North American Jews are so used to the practice today that they may not realize that to most Jews around the world, a flag seems out of place in a house of worship.

“We are so familiar with this in America, it’s so common whether it’s a Reform synagogue, Conservative and even some Orthodox [synagogues], that we take it for granted, it’s almost unnoticed,” said Zola. “But when you travel the world, you begin to realize, ‘Gee, this isn’t the way it is everywhere.’

Josefin Dolsten writes for the JTA global news agency and wire service.