LONDON — After years of North Korea thumbing its
nose at the international community, on Friday Defense
 Secretary James Mattis appeared to signal enough
was enough.
"Right now, [North Korea] appears to be going in a
 very reckless manner … and that has got to be
 stopped," Mattis said at a press conference in London.
He didn't give any details about how the administration
of President Donald Trump plans to deal with the
 reclusive nation, which, under Kim Jong Un, has
drastically increased its missile and nuclear-testing program.
 Mattis Calls North Korea's Conduct 'Reckless' 1:38
But Mattis' remarks continue a recent trend of Trump
 officials taking a harder line on North Korea.
Earlier this month, Secretary of State Rex Tillerson 
said that the "diplomatic … efforts of the past 20 years
 to bring North Korea to a point of de-nuclearization
 have failed."
He also said that military action was "on the table."
Many experts say that Trump's options are limited,
Kim has pledged to develop weapons capable of
striking the U.S. and its allies. Three of the country's
nuclear tests were completed under his rule and he
 conducted more missile tests over the past four years
 than in the rest of the country's history.
Trump could try to levy more sanctions on the country,
 although these have not stopped previous tests and
Tillerson appeared to dismiss this approach earlier
 this month.
But a full-scale invasion would be unlikely — not to
 mention extremely difficult — according to U.S.
 Army strategist Maj. ML Cavanaugh.
Cavanaugh wrote an article in the Modern War 
Institute at West Point, which is a research center
 of the United States Military Academy, warning of
North Korea's tough, "Afghanistan-like geography"
and an army that could act like "a much better-trained,
 much better-armed version of the Taliban."
An American invasion would also carry the risk of a
retaliatory missile strike against America's allies,
South Korea and Japan. The South Korean capital
of Seoul, with its population of 10 million, is just
50 miles from its border with the North.
 FROM MARCH 22: North Korea launches 3rd test missile since Trump took office 2:05