NEW YORK — When Babe Ruth barnstormed across Japan in November 1934 with a team of American All-Stars, he was welcomed not only as a baseball hero, but also as a broker of friendship between two nations drifting toward war.

The 18-game exhibition tour, hailed by politicians on both sides as a chance to promote goodwill, is the subject of “Banzai Babe Ruth,” Robert Fitts’ third book about Japanese baseball history.

“Ruth understood the importance of the tour for Japanese-American relations,” Fitts told Kyodo News. “He rose to the occasion and became an ambassador for the United States for the month he was in Japan.”

Although the 1934 tour was a hit, drawing enthusiastic crowds to see Ruth, Lou Gehrig, Jimmie Foxx and the other American stars go undefeated against a team of top Japanese players, baseball could not prevent the looming crisis. Fitts details an extremist plot to murder the tour’s organizer and plans to stage a bloody military coup while Ruth and his teammates were still in the country.

“‘Banzai Babe Ruth’ focuses on a month with a lot of back story,” Fitts said. “I did two years’ worth of research before I started writing. I wanted to take the facts and present them as a story.”

Fitts, 46, first took an interest in Japanese baseball when he lived in Tokyo in the early 1990s, finishing his American archaeology dissertation while his wife worked for an international law firm. He collected Japanese baseball memorabilia in his free time and played infield on a recreational company team.

“Baseball really became my way to get into Japan and introduce myself to the culture, pick up a little bit of the language — enough to carry on a baseball conversation,” Fitts said.

A few years after the couple returned to New York, Fitts started a Website about Japanese baseball cards in 1999. Originally only a sideline to his job as a consulting archaeologist, the Website became a job in itself with the sensation of Ichiro Suzuki’s 2001 rookie year in Seattle. Fitts soon began to prepare biographies of Japanese ballplayers for his American customers.

In 2003, this led to an opportunity to meet and interview the late Wally Yonamine, the first American player after World War II to join the professional league in Japan.

“Wally’s stories were so wonderful and he was such a good storyteller,” Fitts recalled. “Being in Japan in 1951 was so different from Japan today — I was just enthralled. I remember just forgetting about the article I was planning to write, and saying to myself: ‘That’s a book.’

“What I wanted to do was get as many of these guys who played in Japan as possible to talk to me and tell me their stories. That became my first book. It was an oral history of Japanese baseball. “I figured out within a month into it that this is what I really wanted to do. It was creative, it was fun, and I learned things while doing it.”

Fitts followed “Remembering Japanese Baseball” with a full-length biography of Yonamine. His research for “Banzai Babe Ruth” started in 2007, and included two trips to Japan’s Baseball Hall of Fame in Tokyo to pore over primary source material with bilingual research assistants.

“There are lots of asides I could have gone down, but they went too far off the story,” Fitts said.

Among those that made the final cut are stories about the rumored spy career of camera-toting catcher Moe Berg, the blackmail by which Russian refugee Victor Starffin was forced to join the Japanese team, and the legendary performance of 17-year-old pitcher Eiji Sawamura, who held the Americans to one run in the tour’s closest contest. Sawamura, sometimes called the Japanese Cy Young, so impressed the Americans that he was offered a chance to play in the major leagues, but decided to stay in Japan and later died as a soldier in World War II.

Although the 1934 tour could not forestall conflict, it remains a memorable early example of Japanese-American friendship on the baseball diamond in an era of explosive politics. Fitts shows how the tour ultimately led to the founding of the Tokyo Giants and the creation of a Japanese professional league.

The first player to come from Japanese pro ball to the majors, pitcher Masanori Murakami of the 1964 San Francisco Giants, is the subject of Fitts’ next research project.

“Banzai Babe Ruth” was published in March.