Kirk Spitzer

USA TODAY

TOKYO — World leaders threatened new sanctions against North Korea after Wednesday's reported test of a hydrogen bomb. Yet if history is a guide, even the toughest new measures won't have much effect on the isolated and defiant regime.

North Korea has been under a variety of U.N. and other sanctions since 1993, including arms embargoes, bans on imports of luxury goods and restrictions on international banking. Those measures were imposed to impede the country's nuclear weapons and ballistic missile programs and punish other aggressive actions against its neighbors.

North Korea just shrugged them off, depending on vital economic help provided by neighboring China.

READ MORE:South Korea says it will resume anti-North broadcasts

"Very little economic interaction and trade exists between North Korea, the U.S., Europe or Japan, respectively — hence, the economic impact of past and new sanctions remains limited," said Sebastian Maslow, an assistant professor of law at Tohoku University, who has studied the relationship between North Korea and its neighbors.

"In fact, intensified trade relations between China and North Korea have improved the economic situation in the North while undermining the international sanctions regime," he said.

That may change. China, which remains North Korea's main ally and biggest trading partner, joined the United States in supporting a U.N. resolution condemning Wednesday's test.

China, which provides food and fuel to its neighbor, has not said whether it will impose economic sanctions on the reclusive state, whose erratic behavior has served Chinese interests. The government in Beijing has long valued the buffer zone that North Korea provides with South Korea — and the 25,000 U.S. troops based there — and it fears the chaos that could accompany the collapse of the North Korean regime and the potential flight of millions of North Koreans across the border into China.

In South Korea, the government said Thursday it will resume cross-border propaganda broadcasts because of the test. Seoul said the broadcasts, which North Korea considers an act of war, will begin Friday.

U.S. House Speaker Paul Ryan said Thursday that the House will soon take up legislation that would impose stiffer penalties on countries that do business with North Korea, a move that would hit China the hardest.

The bill would allow the government to freeze assets held in the United States by companies that help fund North Korea's nuclear program by providing the regime with hard currency. Similar legislation passed the House two years ago but was not approved by the Senate.

The current sanctions program dates to July 2006 when, after a series of long-range ballistic missile tests, the U.N. banned all member states from doing business with North Korea involving materials, technology or financial resources related to the country's ballistic missile or weapons of mass destruction programs.

Just three months later, North Korea conducted its first nuclear weapons test. The U.N. responded by expanding the embargo to include weapons and spare parts, and luxury goods. It also froze North Korean financial assets and banned overseas travel for those involved in the country's weapons programs. The sanctions were further tightened in 2009.

Nonetheless, the North has tested nuclear weapons four times since 2006, including Wednesday's explosion that the North described as its first test of a powerful hydrogen bomb. The United States and other governments doubt the claim, saying evidence suggests North Korea detonated a much smaller and less powerful atomic bomb.

Japanese Prime Minister Shinzo Abe was among the world leaders calling for new sanctions following the test, even though Japan's own sanctions have had limited effects.

In March 2010, Japan directed citizens not to to travel to North Korea, banned the entry of North Koreans, barred North Korean ships from Japanese harbors and prohibited other trade with North Korea.

5 reasons North Korea is a 'rogue regime'

Those moves followed the sinking of a South Korean warship by North Korean forces. The sanctions also reflected widespread anger in Japan over a program dating back to the 1970s in which North Korean agents kidnapped at least 17 — and possibly many more — Japanese citizens to train as spies for North Korea.

Japan eased those sanctions in May 2014 as negotiations over the abduction issue continued. Still, there has been little progress in returning known victims to Japan or learning the fate of others.

All of which suggests tougher sanctions won't deter North Korea's weapons programs or other misbehavior, said Sean King, an East Asia specialist with the Park Strategies consulting firm in Taipei and New York.

"We will be at this place again and again," King said. "North Korea's nukes program will only end when its regime does."

Contributing: Erin Kelly in Washington

The Nuclear Club: who the 9 members are