WASHINGTON (CNN) -- Sen. Hillary Clinton decided to join her one-time rival's team because she wanted to be part of the "greatest adventure of our century," she said Monday after President-elect Barack Obama named her as his nominee for secretary of state.

Sen. Hillary Clinton addresses the media in Chicago on Monday while President-elect Barack Obama looks on.

"President Kennedy once said that engaging the world to meet the threats we face was the greatest adventure of our century," Clinton said during a news conference in Chicago, Illinois, when Obama unveiled his national security team. "Well, Mr. President-elect, I am proud to join you on what will be a difficult and exciting adventure in this new century."

Clinton said she would work to restore America's position as "a force for positive change" in the world.

"America is a place founded on the idea that everyone should have the right to live up to his or her God-given potential. And it is that same ideal that must guide America's purpose in the world today," she said.  Watch Clinton accept Obama's offer Â»

During the news conference, Obama called Clinton a woman of "extraordinary intelligence and toughness" who will "command respect in every capital."

"Hillary's appointment is a sign to friend and foe of the seriousness of my commitment to renew American diplomacy and restore our alliances," Obama said.

Speculation that Obama would appoint his former rival for the Democratic presidential nomination to the nation's top diplomatic post surfaced after the two meet secretly in Chicago in mid-November.

When Clinton's name was first mentioned for secretary of state, the Obama team reviewed the relationships her husband, former President Bill Clinton, had forged as part of his charitable foundation work. The Obama team was concerned that the relationships could create conflicts of interest.

To address those concerns, the former president agreed to disclose the names of the more than 200,000 donors to his presidential foundation, a move he had previously resisted, Obama aides told CNN on Sunday.

He also agreed to separate his work with the Clinton Global Initiative from his foundation work and submit the text of future speeches and other activities to State Department officials for review, the Obama aides said.

In a statement, President Clinton said he was "deeply proud" that Obama has chosen his wife to be secretary of state.

"She is the right person for the job of helping to restore America's image abroad, end the war in Iraq, advance peace and increase our security, by building a future for our children with more partners and fewer adversaries, one of shared responsibilities and opportunities," he said.

During the presidential campaign, Obama and Clinton traded tough statements on foreign policy, but, now, Obama and Clinton will be in the same administration, albeit one led by Obama.  Watch more about the other members of the security team Â»

In a now famous ad that showed a telephone ringing at 3 a.m., Clinton challenged Obama's readiness to handle foreign policy crises. Later, Obama questioned Clinton's argument that she had more foreign policy experience.

But during the news conference, Obama dismissed any lingering resentment between himself and Clinton as a result of the tough campaign.

Clinton and the other members of the national security team "would not have agreed to join my administration -- and I would not have asked them to be part of this administration -- unless we shared a core vision of what's needed to keep the American people safe and to assure prosperity here at home and peace abroad," he said.

Obama said there was not a "light bulb moment" when he decided to ask Clinton to be his secretary of state but would not reveal details on the talks that led up to him asking his former rival to join his team.  Watch Obama praise Clinton's abilities Â»

"I have always admired Sen. Clinton. We have worked together extensively in the Senate," Obama said.

"After the election was over and I began to
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