Tensions ratchet up between North Korea and the United States. On April 24, Pyongyang added a threat to sink a U.S. aircraft carrier and accompanying ships to the regime’s constant boasts.

This may be a new specific item, but is part of the usual nonstop barrage of propaganda. The latest threat with the maritime twist is in response to the movement of a U.S. Navy strike group led by the aircraft carrier USS Carl Vinson to the Korea Peninsula.

On the same day, President Xi Jinping of China urged caution in a telephone conversation with President Donald Trump. Adding further to growing tensions, Pyongyang suddenly seized a university teacher with both South Korean and U.S. citizenship as he was about to board a plane out of the country. Finally, there is concern North Korea is about to detonate another nuclear device.

In moving forward, U.S. government officials should keep in mind three basic realities. First, for years North Korea has been characterized by erratic, inconsistent behavior. In 2013, North Korea announced a “state of war” with South Korea and threatened nuclear attack. Pyongyang abruptly abrogated the 1953 armistice agreement ending the Korean War, and cut the military “hot line” communications link with the south.

North Korea also temporarily prevented South Korean workers from entering the Kaesong industrial center, located 6 miles north of the DMZ. But there was no war, Kaesong was reopened, and Pyongyang made positive moves including reunion of separated families. In 2016, South Korea shut down Kaesong.

Second, we must demonstrate commitment to defense of South Korea, our own readiness, and willingness to use a range of forces. The Obama administration rightly deployed the THAAD (Terminal High Altitude Air Defense) anti-missile system for this purpose. In 2013, the Pentagon expanded anti-ballistic missile defenses on the U.S. West Coast. Simultaneously, THAAD was sent to Guam, a potential target. In 2009, THAAD was sent to Hawaii for the same reason.

On cue, China expressed indignation about the deployment. That was predictable, and understandable given potential use of the system’s radars for information gathering. Now, however, Beijing is actively working to restrain Pyongyang, including suspending airline flights between the two cities.

Third, we should emphasize coordination with other nations, including China and Russia if possible, but especially our close friend and ally South Korea.

South Korea’s substantial investment in and trade with China grows, while North Korea remains a costly, dependent though allied communist state. China’s President Xi visited Seoul soon after taking office. He has not visited North Korea.

China’s foreign policy reflects self-interest, and traditional caution regarding military force. North Korea is a drain, and now a source of constant well founded anxiety regarding war.

The frustrating Korean War, from 1950 to 1953, devastated the Korean Peninsula, made the Cold War global, and undercut President Harry Truman. However, Truman’s courageous decision to support the United Nations in defending the south against military invasion from the north laid the foundation for today’s remarkably successful Republic of Korea.

The capstone of transition to democracy was the election of Kim Dae-jung as president in 1998. He completed his 5-year term, and in 2000 received the Nobel Peace Prize. During the earlier dictatorship, Kim survived imprisonment and at least one attempt to kill him. Recent political turmoil has reconfirmed South Korea’s democratic institutions.

As in the past, U.S. leaders should work with allies, underscore military commitment, and pursue diplomacy.

-- Arthur I. Cyr is Clausen Distinguished Professor at Carthage College and author of “After the Cold War.” Contact at acyr@carthage.edu.