During his five months at the United Nations, U.S. Ambassador John Danforth (search) has focused on one goal — bringing peace to Sudan, which has been engulfed in war for 21 years.

Danforth, who resigned Thursday, didn't achieve this aim. But he did get a promise from southern rebels and the Sudanese government to end their long civil war by the end of the year, though no solution to the more recent deadly conflict in the western Darfur region.

Danforth had been mentioned as a successor to Secretary of State Colin Powell, but President Bush chose Condoleezza Rice (search).

Danforth sent his letter of resignation on Nov. 22, six days after the Rice appointment, saying he wanted to retire with his wife, Sally, to his home in St. Louis on Jan. 20 when Bush's first term ends. The president responded with a letter on Nov. 27 accepting his resignation, said U.S. spokesman Richard Grenell.

"Forty-seven years ago, I married the girl of my dreams, and, at this point in my life, what is most important to me is to spend more time with her," Danforth wrote. "Because you know Sally, you know my reason for going home."

Mrs. Danforth suffered a serious fall about 1 1/2 years ago and still suffers from the after-effects.

Danforth, 68, a Republican and former Missouri senator, has been tapped by presidents of both parties as a troubleshooter. He told Bush "not to hestitate" to call on him for short-term projects.

Danforth arrived at the United Nations (search) in early July to replace John Negroponte who went to Baghdad as the first post-Saddam U.S. ambassador to Iraq's transitional government.

After the bitter divisions in the U.N. Security Council over the war in Iraq, the arrival of a new U.S. ambassador was viewed by many diplomats as a fresh start.

In recent months, he has been pressing U.N. Secretary-General Kofi Annan to send more election staffers to help with the Jan. 30 vote. Annan recently raised the ceiling on U.N. international staff allowed in the country from 35 to 59, but won't go higher because of escalating violence — to the annoyance of U.S. officials.

But unlike Negroponte, whose time at the United Nations was consumed by the aftermath of the Sept. 11, 2001 terrorist attacks and the war in Iraq, Danforth was consumed by Sudan, though he spent time on other African problems and also worked hard to strengthen the U.N. machinery to fight terrorism.

Last month, when he presided over the council as its president, Danforth organized a council meeting in Nairobi — only the fourth outside New York since 1952 — to pressure southern rebels and the Sudanese government to end their war.

Danforth's outgoing personality made him personally popular with both the press and his fellow ambassadors, though many disagreed with U.S. policy, particularly on the Israeli-Palestinian conflict.

In early October, he vetoed an Arab-backed Security Council resolution condemning an Israeli raid in Gaza. He called it "lopsided and unbalanced," because it did not mention Palestinian rocket attacks.

Looking back on his U.N. stint, Danforth told the president in his letter, "It has been an important time to be in this position, especially as we attempt to enlist greater U.N. participation in the future of Iraq, and as we advance the interest you have personally shown in helping the desperate people of Sudan."