YANGON, Myanmar — In a historic breakthrough, President Barack Obama on Monday stepped onto the soil of long-shunned Myanmar and into the flag-waving embrace of its once repressed people. "You gave us hope," he declared, the first U.S. president to visit what not long ago had been an international outcast.

Tens of thousands of people poured into the streets to welcome Obama to a place still learning its basic freedoms.

Speaking to a national audience from the University of Yangon, Obama offered a "hand of friendship" and a lasting U.S. commitment, yet a warning as well. He said the new civilian government must nurture democracy or watch it, and U.S. support, disappear.

The visit to Myanmar was the centerpiece of a four-day trip to Southeast Asia that began in Bangkok and will end Tuesday in Phnom Pehn, Cambodia, where Obama will attend an East Asia Summit.

Obama seemed to revel in the history of what he was witnessing in Myanmar — a nation shedding years of military rule, and a relationship between two nations changing fast.

"This remarkable journey has just begun," he said.

In a notable detour from U.S. government policy, the president referred to the nation as Myanmar, the preferred name of the former military regime and the new government, rather than Burma, the old name and one favored by democracy advocates and one commonly used by U.S. officials.

On his first post-election trip abroad, Obama got a warm welcome in Myanmar, hugging long-time opposition leader Aung San Suu Kyi as a personal inspiration to him.

Crowds swelled at every intersection, yelling affectionately for Obama and Secretary of State Hillary Clinton. "You are the legend hero of our world," one banner read.

In his speech, Obama acknowledged Myanmar's many democratic shortcomings but said: "The United States of America is with you."