North Korea is like a bully in the schoolyard, a notion understood in many places around the world, but no one has yet figured out a way to make him behave for fear of causing a war to erupt.

Ever since the end of the Korean War in 1953, North Koreans under dictator Kim Il Sung and then Kim Jong Il, his son and successor, have repeatedly provoked South Korea, the U.S. and Japan with assassinations, more armed violence, infiltration and kidnapping. The North Koreans have blandly denied the provocations or shrugged them off.

Diplomatic protests, economic sanctions and pleas to the United Nations have all come to naught. Even China and Russia, Pyong-yang's allies, have been ineffective in restraining the Kims. The Chinese were evidently unsuccessful in persuading Kim Jong Il, who visited Beijing last week, not to be reckless.

The latest aggravation has been the sinking of a small South Korean warship, the 1,200-ton corvette Cheonan, presumably by a torpedo fired by a North Korean submarine in waters west of the Korean peninsula. In that incident on March 26, about half of the crew, 46 sailors, died.

The government of President Lee Myung-bak in Seoul has been ultra-cautious in response, asserting that a thorough investigation must be completed before action is taken. He was quoted by The Associated Press last week: "What is obvious so far is that the Cheonan did not sink due to a simple accident." The U.S. has taken a similar stance.

The Cheonan affair appears to be falling into a pattern set more than a half-century ago when North Korean agents hijacked a South Korean airliner flying from Pusan to Seoul and forced it to fly on to Pyongyang. Then North Korean MiG fighter planes attacked a U.S. RB-47 reconnaissance plane over the Sea of Japan but were fought off.

North Korean provocations intensified in the 1960s and continued into the 1990s. In 1968, commandos sneaked through the 4,000-meter, wide demilitarized zone that divides the peninsula and got close to the Blue House, the South Korean president's residence, in a raid to assassinate President Park Chung Hee.

About 36 hours later, North Korea captured the U.S. intelligence ship Pueblo in international waters. The crew was released a year later but North Korea still has the ship, which is shown off to tourists. Later that year, 131 commandos infiltrated South Korea for sabotage. The following year, North Korean MiG fighters shot down a U.S. EC-121 electronic intelligence plane on international waters, killing 31 Americans.

In 1974, a North Korean agent attempted to assassinate President Park Chung Hee during a public speech but instead murdered his wife, Yuk Young Soo. (This correspondent was an eyewitness to that tragedy.) Along the demilitarized zone, two American officers were killed by North Koreans wielding axes. The first of at least four North Korean tunnels burrowing under the DMZ was discovered.

A North Korean bomb intended to kill President Chun Doo Whan in Rangoon in 1983 missed him but killed 17 senior South Korean officials. Another North Korean bomb downed a South Korean airliner flying from Baghdad to Seoul in 1987, killing 115 passengers and crew. North Korea fired a missile over Japan in 1999, the first of several firings that some might consider an act of war.

Interspersed in this have been innumerable kidnappings of South Korean and Japanese citizens, unending attempts to infiltrate commandos into South Korea, and repeated discoveries of North Korean spy rings, some with 400 agents in South Korea. Similar intelligence actions have been uncovered in Japan.

Since diplomacy and mild threats have not worked, maybe it's time somebody punched the bully in the nose, just enough to make it bloody but not so hard as to trigger a war.