A series of little-noticed moves has given new momentum to Japanese Prime Minister Shinzo Abe’s push to revise the nation’s pacifist constitution, potentially allowing Japan’s military to use offensive force against other nations for the first time since World War II.

The latest shift came last week when the prime minister’s hawkish new defense minister said the military had begun training for new missions overseas such as U.N. peacekeeping deployments, roughly a month after Mr. Abe himself had declared a reinterpretation of Japan’s existing constitution to allow Japanese forces for the first time in decades to come to the defensive aid of allies under attack.

While Tokyo already has a history of participating in joint military exercises with the United States, the recent round of posturing has drawn sharp reactions from other powers in North Asia, particularly China, where authorities remain leery of a fully remilitarized Japan and its impact on the balance of power in a region still marked by unsettled historical and territorial disputes.

Most U.S. analysts, however, say the recent moves, as well as the Abe administration’s overall push toward revising the constitution, have been a long time in coming — and that the likely result will be a much-needed expansion of U.S.-Japan military cohesion during the years ahead.

“I don’t think we should be worried that Japan is moving toward having a more operationally capable, deployable military that can work with partners in a common, collective self-defense,” said Michael Auslin, the director of Japan studies at the American Enterprise Institute in Washington.

“This has been coming about slowly over decades, and its something we’ve been encouraging the Japanese to do because we want them as a liberal, democratic state and ally of the United States, playing a larger role in maintaining security in Asia and beyond,” he said in an interview.

But rewriting the famous and unique Article 9 of Japan’s constitution, which explicitly prohibits the use of military force to resolve disputes with other nations, would require a nationwide referendum after a two-thirds majority vote in both houses of Japan’s parliament.

While it has for decades been a far-off concept that Japanese lawmakers might one day redraft the document’s post-World War II pacifist underpinnings — the situation suddenly changed with the result of last month’s parliamentary elections in Japan.

A sweeping victory by the ruling Liberal Democratic Party (LDP) gave Mr. Abe a parliamentary supermajority — a reality that triggered wary reactions across Asia.

With memories of Japan’s occupation for much of the first half of the 20th century, South Korea’s major daily newspapers carried front-page articles on the looming prospect of constitutional reform.

“Japan has now entered the path of a country that is able to wage war after discarding [the] pacifist Constitution it has retained for nearly 70 years after the war,” said South Korea’s Kyunghyang Shinmun newspaper.

There was also widespread speculation that longtime Emperor Akihito’s hints that he would like to step down are a veiled warning to Mr. Abe and Japan’s nationalists to go slow in any drive to revise the pacifist clauses in the constitution.

Uncertain future

U.S. analysts say the path ahead is not certain.

“The LDP-led coalition emerged from the summer Upper House election with a supermajority in both houses, and Prime Minister Abe has as much power as he is likely to between now and 2019, when he would presumably have to step down,” said Patrick Cronin, who heads the Asia-Pacific Security Program at the Center for a New American Security in Washington.

“But there is nothing certain or likely when it comes to something such as revising the constitution,” he said. “Democratically elected leaders have numerous brakes on their power, and Abe is a successful politician who makes pragmatic choices and necessary compromises when faced with obstacles preventing him from achieving 100 percent of his goals.”

At the same time, Mr. Cronin said, what the Abe administration is doing is “not a play for war, but a defensive move to preserve Japan’s interests amid a rising China and a less dominant United States.”

He added that the U.S. “will have to remain actively engaged” to ensure that Japan’s “move toward greater defense normalization and a larger defense role for Japan remains consonant with U.S. interests.”

Bruce Klingner, the senior research fellow for Northeast Asia at The Heritage Foundation, said Japan’s military reforms “are good, not scary, long overdue, and many were things that previous leaders had promised and not delivered.”

“The U.S. has been pushing Japan for decades to do more,” said Mr. Klingner.

The Tokyo-based Nikkei Asian Review reported this week that Japan’s Ground Self-Defense Force staged a large-scale, live-fire drill near Mount Fuji simulating the recapture of an island — at a time when Beijing and Tokyo have sparred over island outcroppings in the seas of Japan’s coast. Some 27,000 people watched the maneuvers, including Defense Minister Tomomi Inada, the well-known defense hawk Mr. Abe appointed early this month.

Japan’s military strategic thinking also appears to be anticipating a more normal military future, and the possibility of conflict with China and other regional powers. An annual defense “white paper” approved by Mr. Abe’s cabinet in early August criticized at length Beijing’s increasingly assertive military actions in the South and East China Seas as “dangerous actions that could trigger unanticipated situations.”

The paper called on Beijing to accept a recent international arbitration ruling that found China breached the Philippines’ sovereign rights by endangering its ships and fishing and oil projects.

But it also accused China of stepping up activity around Japan-controlled islands that Beijing also claims in the East China Sea — islands that Tokyo calls the Senkaku chain, while the Chinese call them Diaoyu. The defense policy paper specifically said China’s escalating military activity in the area had caused Japan to scramble defensively against Chinese warplanes — something allowed under the existing Japanese constitution — more than 570 times during 2015.

Beijing angrily denounced the report, accusing Japan of seeking to sow discord between China and its neighbors.

Japan’s new defense blueprint was “full of lousy cliches, makes irresponsible remarks on China’s normal and legal national defense and military development [and] hypes up the East and South China Sea issues,” China’s Defense Ministry said in a statement. “The ultimate objective of Japan is to cook [up] excuses for adjusting by leaps and bounds its military and security policies and accelerating its arms expansion, even rewriting the pacifist constitution.”

Analysts say Beijing’s reaction stems mainly from fear that any constitutional change will draw Japan closer to Washington militarily.

“I don’t think there’s any surprise that the Chinese are worried about a more active and, in fact, more capable Japanese military, and one that is able to be more of a partner with the United States,” said Mr. Auslin. “The Chinese would object to that because they object to what the U.S. is doing in Asia. They talk about it as destabilizing and provocative.”

China, he added, “does not recognize that so much of the opposition it’s facing in the region is actually based on its own actions — that by moderating its own behavior and belligerence in the South or East China Sea, it would most likely cause other nations in the region to be just as moderate.”