Defense Secretary Jim Mattis warned Monday that a North Korean missile launch at the United States, including its territory of Guam, could escalate quickly into war.
The U.S. military is capable of judging where any regime missile is headed "within moments" and would immediately try to shoot down one aimed at the U.S. mainland or one of its territories, Mattis told reporters at the Pentagon.
 
"I think if they fire at the United States it could escalate into war very quickly, yes, that's called ‘war' if they shoot at us," he said. "They shoot at the United States, I'm assuming they hit the United States … if they do that then it's game on and we have to try our best to make sure it does not hit the United States, but we will know that's where it's going."
Mattis said he would not speculate on any military response to North Korea firing missiles in the vicinity of Guam and that any decision would be up to President Trump.
North Korea has said it may finalize a plan this week to fire four missiles that would land 19 to 25 miles in the waters near the island, which is home to 160,000 people and two key U.S. military bases, amid rising tensions over its pursuit of nuclear-tipped intercontinental ballistic missiles capable of targeting the American mainland.
Not longer after Mattis made his remarks on Monday, the Korean Central News Agency reported that Kim Jong Un had been briefed on the plan to bring "enveloping fire" to the Pacific Island, according to the Associated Press. He praised the military's "close and careful plan" while inspecting the Korean People's Army's Strategic Forces.
Trump warned last week that the regime will face "fire and fury" if it continues with its provocations.
Meanwhile, Mattis, Secretary of State Rex Tillerson, and Joint Chiefs Chairman Gen. Joseph Dunford have also been pursuing a diplomatic solution with the North.
Dunford arrived in China Monday to meet with his counterpart on the unfolding crisis on the Korean Peninsula.

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However, there's a couple of things I'm still not clear about. What if they are firing blanks (unarmed missiles? Does that still begin a war?

LIkely the answer to this question is yes because we don't know for sure when they fire these missiles over JAPAN towards Guam whether they are armed missiles or not and likely it means Japan or Thaad (anti missile missiles) at some point might take them out. But, if they are armed this could make a serious radiation mess. Or even if they are not armed it could create a serious radiation or chemical mess wherever the pieces shot up land too.

So, at that point just shooting over Japan towards Guam then is going to begin a war according to Mattis.