SEOUL, South Korea — For more than 60 years, a US-imposed constitution has barred Japan from raising a standing army. Instead, it has been forced to rely on American troops for protection.

But that could soon change.

In an election on Sunday, the ruling coalition — consisting of the right-wing Liberal Democratic Party (LDP) and a centrist ally — landed a pivotal majority in the upper house elections.

The bloc swept 76 of the 121 contested seats, giving it a combined 135 seats in the 242-seat chamber, although the Liberal Democrats fell short of winning a majority.

Analysts say the victory signifies a step forward. Japan, the world’s third-largest economy, has long been plagued by deadlock and dysfunctional politics. The country has had seven prime ministers since 2007.

But for the first time since then, the coalition controls both houses of the Diet, Japan’s parliament. Prime Minister Shinzo Abe, a hardened nationalist elected in September 2012, could become the nation’s first stable leader in years.

Beyond economics, the victory gives Abe the clout to pursue his vision: a bolder Japan, enriched by the expansion of the military and a newfound sense of strength.

Such talk has skeptics, however.

The conservatives have entertained the idea of setting up a standing army since the 1950s. They haven’t succeeded, even though they held power uninterrupted from the mid-1950s until 1989, and have regained their footing in Japanese politics on and off since then.

Japan’s 1947 Constitution, written by American advisers after World War II, imbued a philosophy of liberal democracy and non-aggression. It bars the nation from setting up a traditional military that can address international disputes with force. But the document permits a limited, civilian-run “self-defense force.”

Despite bitter wartime hostilities, a US security guarantee allowed Japan to focus on economic development. That has enabled it to grow wealthy without having to spend on a significant military force.

But times are changing. An ascendant China, which has laid claim to the disputed Senkaku Islands, is riling Japanese nationalists and giving them reason to inject muscle into the military.

To realize his military vision, Abe will need to play a clever political game that includes first-ever revisions to the constitution.

Under the current system, Abe needs to muster a two-thirds majority in the Diet just to start constitutional proceedings. The LDP-led coalition holds enough seats in the lower house, but not in the upper house.

If both chambers concur, a national referendum would be held to decide on constitutional changes.

To bypass the stiff requirements, the LDP wants to enact a separate constitutional reform to lower the threshold to a 51 percent majority — undoing the two-thirds vote now needed.

The idea of constitutional reform carries some popular support, although it’s not entirely clear if the measure would pass, according to polls.

For its part, the Japanese electorate is far more concerned about the economy, which is why Abe’s party was so widely supported.

For two decades, Japan has been home to a sclerotic economy, soaring national debt levels, and increasingly high youth unemployment. Leadership instability during much of that time has left lawmakers unable to address these problems, critics say.

Since April, the premier has been trying to breathe life into the economy with his trademark policy known as “Abenomics.” It’s a three-pronged plan consisting of monetary easing, fiscal stimulus and structural reforms, intended to get markets moving again. Voters will no doubt demand that Abe follow through on an economic reinvigoration.

On Sunday, Abe told reporters that he’ll meet their expectations for a better business climate. “It is not easy to steer Japan out of 15 years of deflation, but we will not have a sound welfare system, national security or diplomacy, unless we have a strong economy,” he said.

Beyond the economy, more immediate factors could slow down the path to militarization.

It’s unclear whether the LDP’s centrist coalition partner — hardly a nationalist party — will throw its weight behind the idea. And a bolder Japan risks alienating key allies, like South Korea and the US.

This year, Seoul has accused Tokyo of rewriting the history of Japanese war crimes. In May, the Korean foreign ministry rebuked the statements of one conservative mayor, who proclaimed that Japanese soldiers needed Korean sex slaves for relaxation in World War II.

Regional neighbors also objected when in April a delegation of Japanese ministers visited the Yasukuni Shrine, a controversial site where many Japanese war criminals are buried. When asked on Sunday, Abe would not say whether he has plans to visit the shrine.

Another issue is the cost of raising an army. Next year, Japan’s national debt is expected to approach 240 percent of GDP, more than twice that of the US. Engaging in a costly arms race with China could weaken the country.

Pursuing a military, therefore, may not be Japan’s best option in projecting strength.

“Anything Japan can do to further strengthen and liberalize its economy lessens, or at least delays, a sense of inevitable Chinese economic hegemony in Asia,” said Sean King, vice president at Park Securities in New York.

Investors are urging Japan to enact reforms needed to join the Trans-Pacific Partnership (TPP), a free-trade network of Asian countries spearheaded by the US. The bloc is designed, in part, to offset Chinese influence.

“By following through on joining TPP, Japan would become an even more valued partner to the United States in balancing China's reemergence,” King concluded.

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