In recent years, the changing nature of war, with hazy battle lines, shifting alliances and stateless antagonists, has been matched with a new breed of reporter, many of whom, like Mr. Foley, operate without the backing of a traditional news organization. Conflict reporting, said Philip S. Balboni, the president and chief executive of GlobalPost, one of the outlets that had published Mr. Foley’s work, seemed to grow progressively more dangerous with the war in Libya that began in 2011. That war, like others that have followed in Syria and Iraq, had “no front lines and no established players.” The seasoned war photographers Chris Hondros, of Getty Images, and Tim Hetherington, of Vanity Fair, were among those killed there.

In remarks on Wednesday, President Obama condemned those who had killed Mr. Foley, and vowed that they would be brought to justice. “The world is shaped by people like Jim Foley,” he said.

According to the Committee to Protect Journalists, 32 journalists, including Mr. Foley, have been killed so far in 2014, compared with 70 in 2013 and 74 in 2012. But the committee’s deputy director, Robert Mahoney, noted that in 2013, at least 65 journalists went missing, more than twice as many as in the preceding two years combined. More journalists are also being imprisoned, he said, in places like in Egypt where 13 are currently in jail.

Foreign journalists were initially welcomed in Syria. But the conflict soon turned, and they began to be seen as interlopers, then as targets. At least 69 other journalists have been killed since the beginning of the conflict there in the wake of the Arab Spring of 2011, the committee said. More than 80 have been kidnapped, and about 20 remain in captivity, the group said, though precise numbers are hard to pin down because many incidents go unpublicized.

Many of those taken captive have been freelance journalists hoping to carve out careers by reporting where others had feared to tread. Mr. Foley, 40, was among them. He had filed stories from the Middle East’s most deadly conflicts for Global Post, Agence France-Presse and others, and had previously been kidnapped in Libya. In a video, he described hostile soldiers coming toward him in that country. “I didn’t want to be the guy who said ‘let’s turn around,’ ” he said. “I didn’t want to do that.”