RICHMOND, Virginia (REUTERS) - Legislation requiring that the Korean name for the Sea of Japan be included in new school textbooks has become law in the US state of Virginia, a victory for Korean-American campaigners backed by the South Korean government.

Virginia Governor Terry McAuliffe signed the law earlier in the week, a spokesman confirmed on Thursday.

The law requires textbooks to add the name "East Sea," as the body of water that separate Japan and Korea is known in Korea.

Passage of the legislation represents a significant victory for vocal campaigners among Virginia's 82,000 Korean-Americans, who greatly outnumber the state's 19,000 ethnic Japanese.

The issue attracted intense lobbying not only from Korean-Americans but the governments of South Korea and Japan more than 7,000 miles (11,000 km) away, which have been squabbling for years over the name for the sea.

It is a source of intense bitterness for Koreans that the "Sea of Japan" was standardised worldwide while Korea was under Japanese colonial rule.

The culmination of what had been a long campaign saw none of the fanfare or emotional fireworks that accompanied the bill's passage through the Virginia legislature in February, when large numbers of ethnic Koreans turned out to back the measure.

Mr McAuliffe had pledged during his campaign for governor that he would sign the legislation if it ever came to his desk.

The law stipulates, "That all textbooks approved by the Board of Education ... when referring to the Sea of Japan, shall note that it is also referred to as the East Sea."

The issue came to a head in Virginia at a particularly strained period of Japan-Korea relations, with South Korea concerned that the government of Japanese Prime Minister Shinzo Abe is seeking to rewrite Japan's wartime past in a less apologetic tone.

The Washington Post reported in January that Japan's ambassador to Washington, Kenichiro Sasae, wrote to Mr McAuliffe late last year urging him to oppose the bill or risk damaging the strong economic relationship between Japan and Virginia.

Mr Sasae noted that Japan was the state's second-largest foreign investor, injecting almost US$1 billion (S$1.26 billion) in the past five years. He said Japanese companies employed about 13,000 people there.

The Japanese Embassy said it had no comment on the approval of the legislation.