JUDY WOODRUFF: But first, war games in Korea. For decades, the U.S. and South Koreans have practiced military exercises, often involving tens of thousands of troops and massive firepower. The U.S. says they're designed to enhance readiness and maintain stability. The drills that started Monday and will continue into next week don't look particularly threatening. But some Korea watchers are calling them provocative.
NewsHour special correspondent Nick Schifrin has this report.
NICK SCHIFRIN: As visuals go, this is as provocative as this month's U.S.-South Korea exercises get. Four men with 15 stars in front of a Patriot missile defense system in South Korea.
GEN. VINCENT BROOKS, U.S. Army: We have had the responsibility of providing military options to our national leaders. And exercises are a way of making sure that the option is a ready option, it's a capable option.
NICK SCHIFRIN: General Vincent Brooks is the U.S.' top commander in South Korea. He is leading exercises that are almost entirely computer simulations, as seen here in the 2013 version. It doesn't look like much, but the exercises allow the U.S. and South Korea militaries to test their communication in case of war.
GEN. VINCENT BROOKS: Being in readiness to fight tonight if we have to is what we'll do.
NICK SCHIFRIN: But exercises the U.S. calls defensive North Korea calls provocative. Today, state TV showed a smiling Kim Jong-un ordering the production of more rocket warheads and engines. And a not so subtle hint on the poster that North Korea is developing a new missile design. North Korea said the exercises were driving the peninsula to war, and vowed to respond.
WOMAN (through interpreter): U.S. warmongers ignored our warning that they should act cautiously and instead made a dangerous military provocation. They will not be able to avoid merciless retaliation and unsparing punishment.
BALBINA HWANG, Former State Department Adviser: To say these defensive, deterrence exercises are the cause of North Korea's insecurity simply have it backwards.
NICK SCHIFRIN: Balbina Hwang is a visiting Georgetown professor and former senior State Department advisor on North Korea. She points out in the last few years, the North Koreans have dramatically increased their missile tests and missile capacities. And it's those tests that make U.S. preparedness crucial.
BALBINA HWANG: It is very important for the U.N. forces, U.S. and South Korea, to be able to maintain constantly, modern, capable defense and deterrence. That is the purpose of the exercise.
NICK SCHIFRIN: But the U.S. and South Korea also conduct annual exercises with massive numbers of forces, and massive amounts of live fire. These are held every spring, and when considered alongside with this month's exercises, the U.S. should acknowledge North Korean anxieties are legitimate, argues Mansfield Foundation President Frank Jannuzi.
FRANK JANNUZI, President, Mansfield Foundation: Every time we are practicing, whether it's field exercises, or even a table top exercise, they get a little bit nervous about what we might do. They also worry about the capabilities that we're demonstrating. And in this particular exercise in the past, we have sometimes demonstrated a capability to launch a decapitation attack, attacking the North Korean leadership.
NICK SCHIFRIN: Jannuzi participated in 2004 talks that froze and dismantled North Korea's nuclear program in exchange for economic assistance. He was a State Department and congressional North Korea policy analyst. He believes these exercises contribute to increased tensions, and that the U.S. should change them to send a signal.
FRANK JANNUZI: Deterrence can be bolstered without flexing our muscles with B-52 bombers, or B-2 bombers, nuclear capable strike aircraft that could annihilate North Korea. We don't need necessarily to practice those martial arts.
NICK SCHIFRIN: Over the last few weeks, some of the tension has cooled. Last night, President Trump even praised Kim Jong-un.
PRESIDENT DONALD TRUMP: I believe he is starting to respect us, I respect that fact very much. Respect that fact. And maybe, probably not, but maybe, something positive can come about.
NICK SCHIFRIN: And North Korea, despite fiery rhetoric, has indicated it doesn't want increased conflict.
BALBINA HWANG: All this talk and rhetoric about shooting missiles and sea of fire and nuclear war, that's talk. But what were the actual actions? We do not see any particular increase in North Korean military readiness for war. We don't see any sort of major maneuvering that would indicate North Korea is ready to launch any kind of major conventional or military strike.
FRANK JANNUZI: A close reading of North Korea's statements has provided signals to the United States that in fact they are open to negotiations, they're willing to sit down and talk with us. We need to test them. And we need to explore what, if anything, is possible through those talks.
NICK SCHIFRIN: And those commanders leading this month's exercise, including Admiral Harry Harris, say they hope their readiness creates room for diplomacy.
ADM. HARRY HARRIS, U.S. Navy: Incredible combat power should be in support of diplomacy, and not the other way around.
NICK SCHIFRIN: So, the U.S. exercises and the North Korean rhetoric will continue. But, from all indications, both sides hope the preparations for war and the threats of war don't lead to war.
For the PBS NewsHour, I'm Nick Schifrin.