Japan's parliament is moving toward final approval of legislation that would loosen post-World War II constraints placed on its military, an issue that has sparked sizeable street protests and raised fundamental questions about whether the nation needs to shift away from its pacifist ways to face growing security challenges.

Opposition parties, in a last-ditch show of resistance, were delaying a vote on the bills by introducing a series of no-confidence measures against government ministers and parliamentary leaders on Friday. They were destined to fail, but ate up hours of time to debate and vote on each one.

Prime Minister Shinzo Abe has made expanding what the military can do one of his legislative priorities in the face of North Korean missile tests, Chinese challenges to Japanese sovereignty over remote islands, and Middle East terrorism. One major goal of the legislation is to allow the military to work more closely with its most important ally, the United States.

The public, while recognizing the threats, remains uncomfortable at best with the changes. Those opposed outnumber supporters by a wide margin in media polls, and rallies against the bills and Abe himself have swelled into the tens of thousands in recent months, unusually large for Japan.

A look at what's at stake:

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HOW WOULD THE LEGISLATION CHANGE JAPAN'S MILITARY?

Japan's post-World War II pacifist constitution restricts the military to defending itself and the country. It's officially called the Self-Defense Forces, or SDF.

The change that has gotten the most attention allows the military to defend allies under a concept known as collective self-defense, which previous governments have considered unconstitutional.

For example, Japan would be able to intercept a missile flying over Japan and headed for U.S. territory. Currently it can shoot down a missile only when fired at Japan. Or, if an American warship came under attack, Japanese forces could come to its defense.

Farther afield, Japan would be able to carry out minesweeping in Mideast waters.

All these activities could only be carried out under certain conditions. For example, the situation must be deemed an "imminent critical threat" to Japan. An interruption to oil shipments could be such a threat to resource-poor Japan, justifying minesweeping in the Mideast.

The opposition says the conditions are overly vague, giving future governments too much leeway to interpret them as they see fit.

The legislation would also allow Japan to do more in U.N. peacekeeping missions, including logistical support for other militaries and protection for civilian workers. Previously, Japan has restricted its role to noncombat activities such as building infrastructure and policing.

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WHY ARE THE CHANGES SO CONTROVERSIAL?

Moves to expand the military's role are almost always contentious in Japan. There was stiff public and parliamentary opposition when Japan first joined U.N. peacekeeping operations in 1992, and when it sent troops to Iraq in 2004 for construction projects.

Many Japanese are wary of any change to the country's pacifist stance, which has brought seven decades of peace and relative prosperity. Some worry that deepening U.S.-Japan security ties will make Japan a more likely target of anti-U.S. extremists, and increase the risk of becoming embroiled in a U.S.-led conflict. Some students worry the legislation could lead to a military draft as Japan's population shrinks and ages.

Backers of the legislation argue that the world has changed, and that a more active military would actually help preserve Japan's peace and prosperity by deterring China and North Korea.

For its part, the U.S. government has welcomed Abe's security legislation as it seeks closer cooperation with Japan, Australia and others in the region to counter Chinese challenges to U.S. hegemony in the Pacific.

Japan has depended on the U.S. for protection since World War II, allowing American troops to be stationed on Japanese soil in return. The U.S. remains treaty-bound to defend Japan, but there is nascent concern that a budget-constrained United States may not be able to or have the political will to do so in the future.