Liberian President Ellen Johnson-Sirleaf has become one of the few women to address a joint sitting of the United States congress.
Mrs Johnson-Sirleaf is Africa's first elected female leader
In a speech which was frequently interrupted by standing ovations, she said US aid was helping to restore peace to Liberia and West Africa.
She promised to make Liberia "America's success story in Africa."
Liberia was founded by freed US slaves in 1847 and many Liberians see the US as their "big brother".
After her speech, congress promised an extra $50m in aid for Liberia, still recovering from 14 years of civil war.
Mrs Johnson-Sirleaf is due to meet President George W Bush next week.
Meanwhile, United Nations Secretary-General Kofi Annan has urged the Security Council not to make big cuts in the 15,000 UN peacekeepers in Liberia over the next few years, because the peace remains fragile.
Mrs Johnson-Sirleaf also thanked Mr Bush for putting pressure on Liberia's former President Charles Taylor to step down in 2003, to end the war.
Some leading US politicians want Mr Taylor to face justice for allegedly backing brutal rebels in neighbouring Sierra Leone.
He is currently in exile in Nigeria but Mrs Johnson-Sirleaf only mentioned his name once.
She said her priorities were reconstruction and reconciliation but "Liberia has little option but to see that justice is done in accordance with the requirements of the United Nations and the broad international community".
Nigeria's President Olusegun Obasanjo has said he will only hand Mr Taylor over to an elected Liberian leader, not to the UN-backed war crimes court in Sierra Leone.
Ed Royce, vice chairman of the US House of Representatives International Relations subcommittee on Africa, on Wednesday said many people were "still waiting" for Mrs Johnson-Sirleaf to ask Mr Obasanjo to keep his promise.