Washington (CNN) The United States and Japan announced big changes Monday to the guidelines that will govern the defense relationship between the two countries going forward.

Under the new guidelines, Japan will be able to defend other countries -- like the United States -- that come under attack, such as if North Korea were to launch a missile toward America.

Coming nearly 20 years since the guidelines were last updated, a senior U.S. defense official said the announcement was a "big deal" and a "very important" moment in the U.S.-Japanese alliance.

"The threat from North Korea is increasing," the official said, adding the new directives could lead to more stability on the Korean peninsula and the Asia-Pacific region.

Officials also said that as the weight of the Asia-Pacific region in global affairs has increased, not to mention the Obama administration's policy of 'rebalancing' the country's focus in that direction, such an update to the U.S.-Japanese alliance was necessary.

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