GWEN IFILL: A big moment for a famed political dissident and her country.
Margaret Warner has the story.
MARGARET WARNER: For Aung San Suu Kyi, one of the world's most celebrated democracy activists, it's the first visit to the United States in more than 40 years.
And, today, the Myanmar opposition leader was honored with the Congressional Gold Medal at a ceremony in the Capitol Rotunda.
AUNG SAN SUU KYI, Myanmar opposition leader: From the depths of my heart, I thank you, the people of America, and you, their representatives, for keeping us in your hearts and minds during the dark years when freedom and justice seemed beyond our reach.
MARGARET WARNER: Congress first granted Suu Kyi its highest award in absentia back in 2008, when she was under house arrest, part of a long ordeal that started in 1989, when the military-led government declared martial law and cracked down on all protest or dissent.
Suu Kyi spent 15 of the next 21 years as a political prisoner. Her determination was apparent when she was released in November of 2010.
AUNG SAN SUU KYI: They have not acted in accordance with the rule of law. And that I shall always fight against, because I don't think that any country can survive as a prosperous and dignified nation unless there is rule of law.
MARGARET WARNER: In January of this year, the Nobel Peace Prize winner announced she would run for parliament. Elections took place in April, and her party, the National League for Democracy, scored a sweeping victory, winning 43 of the 45 seats at stake.
It's now the largest opposition party in the national legislature, though it holds fewer than 10 percent of the seats. All this came as Myanmar, formerly called Burma, moved toward greater openness under new President Thein Sein, once a member of the old military junta.
His government has lifted many press restrictions and released hundreds of political prisoners, but hundreds remain.
And at a Washington event yesterday, Secretary of State Hillary Clinton said the U.S. wants to see even greater reforms.
SECRETARY OF STATE HILLARY RODHAM CLINTON: I think one of the important reasons for her visit at this time is to remind us of how much more still lies ahead, from strengthening the rule of law in democratic institutions to addressing the challenges in many of the ethnic conflicts.
MARGARET WARNER: Washington did restore full diplomatic relations with Myanmar in January. And Derek Mitchell was named the first American ambassador there since 1990.
The Obama administration also has lifted some economic sanctions, allowing for American investment in Myanmar. And it is currently weighing lifting others, including the ban on imports from the Southeast Asian country.
Yesterday, in Washington, Suu Kyi urged a greater easing of U.S. sanctions.
AUNG SAN SUU KYI: I think that our people must start taking responsibility for their own destiny. I do not think we should depend on U.S. sanctions to keep up the momentum of our movement for democracy.
MARGARET WARNER: Her visit also included a private meeting with President Obama at the White House late today. Next, she goes to New York to address the U.N. General Assembly.