Japan's upper chamber of parliament early Saturday gave final approval to a set of controversial bills allowing the country's military to engage in overseas combat assignments -- under certain circumstances -- for the first time since World War II. The lower chamber approved the bills in July.

[Original story, published at 3:46 p.m. ET Thursday]

Japan's upper house of Parliament is poised to pass the first major reinterpretation of the country's pacifist constitution since the end of World War II, despite fierce and vocal opposition that culminated with lawmakers getting into physical altercations.

The historic vote, which could take place Friday, marks the most dramatic shift in Japanese military policy in 70 years, and has triggered the largest protests seen in Tokyo in decades.

A scuffle broke out Thursday as opposition lawmakers in a special committee of the Upper House attempted to delay a vote. But the bill ultimately passed the committee, clearing a key hurdle and setting the stage for a vote on the measure.

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The controversial legislation reinterprets Article 9 of the Japanese constitution, which outlaws war as a means of settling international disputes.

The reinterpretation allows Japan to exercise collective self-defense, enabling the Japanese military, known as the Self-Defense Forces (SDF), to fight overseas and defend allies with limited conditions.

The argument for the bills

Supporters of the legislation, including top U.S. officials, say Japan needs to expand the role of the SDF to counter potential threats from nations such as China and North Korea. Both continue to develop their military and nuclear weapons programs.

Earlier this month, China staged its largest military parade ever to celebrate 70 years since Japan's World War II defeat. Beijing remains locked in territorial disputes with multiple Asian neighbors in the East and South China seas.

Photos: China celebrates World War II victory Chinese military helicopters fly in formation over Tiananmen Square on September 3, 2015 in Beijing, China. A massive military parade in Tiananmen Square marked the 70th anniversary of victory over Japan and the end of World War II. Hide Caption 1 of 19 Photos: China celebrates World War II victory A military vehicle carrying a Pterodactyl I drone rolled through Beijing on September 3. Hide Caption 2 of 19 Photos: China celebrates World War II victory Military vehicles carry missiles past the Tiananmen Gate on September 3. Hide Caption 3 of 19 Photos: China celebrates World War II victory Chinese President Xi Jinping stands in a sedan to address the People's Liberation Army on September 3. Hide Caption 4 of 19 Photos: China celebrates World War II victory Thousands of doves are released during the parade on September 3. Hide Caption 5 of 19 Photos: China celebrates World War II victory Tanks promenade through the parade route on September 3. Hide Caption 6 of 19 Photos: China celebrates World War II victory Chinese veterans wave from a bus during the military parade on September 3. Hide Caption 7 of 19 Photos: China celebrates World War II victory Chinese military helicopters fly in formation during the grand parade on September 3. Hide Caption 8 of 19 Photos: China celebrates World War II victory Missiles are displayed along the parade route on September 3. Hide Caption 9 of 19 Photos: China celebrates World War II victory Chinese soldiers march past the Great Hall of the People at Tiananmen Square on September 3, 2015 in Beijing, China. Hide Caption 10 of 19 Photos: China celebrates World War II victory Chinese President Xi Jinping, in the middle, stands with (from left) South Korean President Park Geun-hye, Russian President Vladimir Putin, and former Chinese presidents Jiang Zemin and Hu Jintao. Hide Caption 11 of 19 Photos: China celebrates World War II victory Chinese soldiers march past the Great Hall of the People in Tiananmen Square on September 3 in Beijing, China. Hide Caption 12 of 19 Photos: China celebrates World War II victory Chinese President Xi Jinping, left, stands with former Chinese Presidents Jiang Zemin and Hu Jintao and current Premier Li Keqiang at the military parade in Beijing on September 3. Hide Caption 13 of 19 Photos: China celebrates World War II victory People's Liberation Army troops arrive at Tiananmen Gate in formation for the parade on September 3. Hide Caption 14 of 19 Photos: China celebrates World War II victory Chinese soldiers march past Tiananmen Square on September 3. Hide Caption 15 of 19 Photos: China celebrates World War II victory A Chinese military choir stands in position ahead of a military parade at Tiananmen Square in Beijing on September 3. Hide Caption 16 of 19 Photos: China celebrates World War II victory Chinese soldiers conduct last-minute drills ahead of the military parade in Beijing's Tiananmen Square on September 3. Hide Caption 17 of 19 Photos: China celebrates World War II victory Decorated with medals, 85-year-old Shen Ji-lan prepares for the military parade in Beijing. She is the only person in China to be appointed twelve consecutive times as a member of the National People's Congress, China's legislature, according to local media. Hide Caption 18 of 19 Photos: China celebrates World War II victory A paramilitary policeman stands at attention in Tiananmen Square in Beijing on September 2, 2015. Hide Caption 19 of 19

On Tuesday, North Korea warned the United States and its allies that it is ready to use nuclear weapons "at any time" and is expected to launch a new satellite using a long-range rocket sometime in the coming weeks.

Tokyo has faced growing international pressure to expand the role of its military to defend the interests of its key allies, including the United States. America is bound by treaty to defend Japan, an agreement that has been in place since 1960.

"Japan is like the 42-year-old kid still living in the basement of the United States," said longtime Asia strategist Keith Henry.

Henry's Tokyo-based consulting firm, Asia Strategy, provides governmental policy analysis. Henry likens the defense bills to Japan finally "growing up" and moving beyond vague concepts of peace and democracy that are no longer practical given today's rapidly changing geopolitical landscape.

Henry says Japan is assuming a more proactive role in regional security, in part to offset China's growing military might.

"Japan is moving out of the house of the U.S. that was essentially built after World War II," Henry said. "But there are risks involved in protecting one's national self interests."

The argument against

Those potential risks have triggered outrage on the streets of Tokyo. Opponents of the legislation say seven decades of Japanese postwar pacifism are simply being tossed away without proper public debate or discourse. They worry about the consequences of potentially sending troops into battle without actual combat experience.

Tens of thousands of anti-war demonstrators have been gathering in recent weeks outside the Japanese Parliament building -- the largest demonstrations of their kind in Japan in more than 50 years. They are students and teachers, workers and retirees, grandchildren and grandparents.

Some wear work attire or school uniforms. Others have T-shirts, bandanas, or posters with spirited slogans like "No war! No Abe!" -- a message to Prime Minister Shinzo Abe -- who has grown increasingly unpopular in recent months for doggedly pushing the controversial security bills through the Japanese parliament.

Abe's face appears on posters with a Hitler-style mustache and Nazi swastika drawn on his forehead. The symbolism is clear. Some of these demonstrators view their Prime Minister as a dictator.

Civic group members hold placards during an anti-government rally in Tokyo on August 23, 2015.

Kazuo Shii, chairman of the Japanese Communist Party and Abe's political opponent, used a loudspeaker to rev up the crowd on Monday evening.

"We fight, fight and fight through it! And abolish these unconstitutional security bills," Shii shouted as the crowd cheered.

Hidenori Shida, a 65-year old IT engineer, said he's frightened by the idea that a Japanese bullet might someday kill someone overseas.

"Japan is a country which pledged not to fight a war again," he said. "We have killed no one in the (past) 70 years. This bill is unforgivable."

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Sweeping government powers?

While the security legislation may strengthen Japan's ties with its allies, Koichi Nakano, a professor at Sophia University, warns it also gives "very sweeping powers to the government," which could allow logistic support and assistance to allied countries during wartime.

He said that Abe's administration has rushed discussion of the security legislation, and that the public "demand(s) the government to slow down so that people get a better understanding of what is happening."

Opposition to the move is clearly evident in opinion polls. A recent poll carried out by Japanese newspaper Asahi Shimbun indicated that 54% of respondents opposed the legislation, while 29% supported the bills. Three-quarters of respondents said parliamentary debate on security bills has been insufficient.

Photos: Shunichiro Kobayashi, 19, joined the protests after learning about them on Twitter. He's worried that Japanese forces will be sent to the Middle East and other conflict zones, and that Japanese military lives could be lost. He also says he fears "economic draft," the trend of youth from poor families being forced to turn to the military for work due to a lack of opportunities. "I am rather poor and studying on scholarship. I am worried that economic draft become more realistic in the future," he says. Hide Caption 1 of 6 Photos: Hiroko Shiomi, a 22-year-old student, traveled from Shiga, west Japan, to take part in the protests. "I made this sign to encourage the people to raise the voice in my region," she says. "I have never seen such a big movement through the country in my life." Hide Caption 2 of 6 Photos: Mana Shibata, from the student protest group SEALDs, says, "We do not know a war, never experienced it. But when talking to grandparents, they say they feel a war is getting closer to us." Shibata says she will continue to speak out about the legislation, even when it has passed by Prime Minister Shinzo Abe. "When we stop saying it, he (be) will become a dictator." Hide Caption 3 of 6 Photos: Hidenori Shida, 65, says he is frightened by the idea that a Japanese military bullet one day might kill someone overseas. "Japan is a country which pledged not to fight a war again, to hold no combat power as a remorse after war. We have killed no one in the (past) 70 years. This bill is not forgivable." Hide Caption 4 of 6 Photos: Pensioner Mie Inomata, 66, is very angry. She said she was at Monday's protest in Tokyo to speak out for others' families and children. "I have a son, and I have many grandchildren," Inomata said. "When I think about the future of my children, as an adult who is alive, I have to take the responsibility to voice my words -- or else I will regret (it)!" Hide Caption 5 of 6 Photos: Married couple Masakazu Suzuki, 65, and Mieko Suzuki, 67, joined the Tokyo demonstration after work on Monday. "The peace constitution formed peaceful post-war Japan. I have taken it for granted, but now I need to wake up and act for the future generation. Japan should contribute to world peace not by the use of force, but by a peaceful way," Mieko says. Masakazu adds, "These bills violate the constitution. We need to replace (Prime Minister) Abe to change Japan." Hide Caption 6 of 6

Economic cost?

There is also concern about the potential impact of the legislation on Japan's defense budget, at a time when the nation is struggling with a crippling national deficit and chronic economic stagnation.

A stronger U.S. alliance and the expansion of SDF missions could force increases in defense spending. Japan's Ministry of Defense submitted a 5.09 trillion yen ($41.7 billion) request for budget allocations for the coming fiscal year, a 2.2% increase from 2015.

The increased spending could continue to bolster the Japanese defense industry, which received a boost after Abe did away with a self-imposed ban on exports of weapons and military hardware dating back to the 1960s.

The changes allow Japanese defense companies to sell to new markets. Analysts say they also allow Japan to become more proactive in its own defense, a move welcomed by the United States but widely criticized by Abe's political opponents and sections of the general public.

Public protests

It's rare for the Japanese public to turn public dissatisfaction with politics into large-scale demonstrations. But massive protests have been a regular occurrence in recent months.

On Monday evening, an estimated 45,000 protesters turned out -- vastly outnumbering the authorities tasked with containing them. They forced their way through police barricades, filling the streets and stopping traffic in front of the Japanese parliament. Despite the chaos, which is unusual in the normally orderly Japanese capital, police did not use force against the demonstrators. Officers made only one arrest and nobody was injured.

The number of street protests in Japan has increased since the March 11, 2011 earthquake, tsunami, and Fukushima meltdown, as the public began questioning the safety of nuclear plants. Anti-nuclear protests have also drawn tens of thousands onto the streets, opposing the government's plan to restart reactors nationwide.

Young voices

Japanese students have reemerged as a powerful force in organizing demonstrations, after years of apathy and absence in political discourse. In May, the Students Emergency Action for Liberal Democracy (SEALDs) was formed and has grown rapidly.

Mana Shibata, a 22-year-old anthropology major and SEALDs organizer, said many young people like her are trying to send a message to Abe and lawmakers that Japan is heading down a "dangerous path."

"When we stop saying it, [Abe] will become a dictator," she claimed.

Shibata was handing out walkie-talkies, buttons, and instructions to other students who gathered ahead of Monday evening's protest. The student activists wore matching T-shirts and held signs they created themselves.

What separates today's protests from the ones in the past is the role of social media. People of all ages are now using Twitter and Facebook to organize and share information.

Nakano has predicted the protests will continue.

"Nobody is going to just go home and start sleeping -- they are awake. And they are trying to build on what the government did, and what the protests have accomplished," he said.