"Anyone who tells you otherwise, anyone who tells you that America is in decline or that our influence has waned, doesn't know what they're talking about," Obama said in his State of the Union address before a joint session of Congress.
The world is changing and the United States can't control every event, he said.
But America remains the one indispensable nation in world affairs -- and as long as I'm president, I intend to keep it that way," Obama said. "That's why, working with our military leaders, I have proposed a new defense strategy that ensures we maintain the finest military in the world, while saving nearly half a trillion dollars in our budget."
He noted he already sent Congress legislation that will secure the country from the growing danger of cyber-threats.
The withdrawal of U.S. troops from Iraq allows America "to strike decisive blows against our enemies," Obama said. "From Pakistan to Yemen, the al-Qaida operatives who remain are scrambling, knowing that they can't escape the reach of the United States of America."
Operating from a position of strength also means the United States has begun winding down the war in Afghanistan, with 10,000 troops already home and 23,000 will leave by the end of the summer. The transition of responsibility to Afghanistan will continue, he said, "and we will build an enduring partnership with Afghanistan, so that it is never again a source of attacks against America."
Obama also noted the changes that have swept across the Middle East and Africa.
A year ago, Libyan dictator Moammar Gadhafi "was one of the world's longest-serving dictators -- a murderer with American blood on his hands. Today, he is gone," Obama said.
In Syria, Obama said he had no doubt President Bashar Assad's regime "will soon discover that the forces of change can't be reversed, and that human dignity can't be denied."
The United States has a "huge stake" in the outcome of the pro-democracy movement, he said.
"While it is ultimately up to the people of the region to decide their fate, we will advocate for those values that have served our own country so well," he said. "We will stand against violence and intimidation. We will stand for the rights and dignity of all human beings. … We will support policies that lead to strong and stable democracies and open markets, because tyranny is no match for liberty."
The United States will safeguard its own security against those who threaten its citizens, friends, and interests, singling out Iran.
"Through the power of our diplomacy, a world that was once divided about how to deal with Iran's nuclear program now stands as one. The regime is more isolated than ever before … and as long as they shirk their responsibilities, this pressure will not relent.
"America is determined to prevent Iran from getting a nuclear weapon, and I will take no options off the table to achieve that goal," Obama said, adding that a peaceful resolution is still possible and preferable.
He reiterated the country's "iron-clad commitment" to Israel's security and said it has meant the closest military cooperation between the two countries in history.
"From the coalitions we've built to secure nuclear materials, to the missions we've led against hunger and disease; from the blows we've dealt to our enemies; to the enduring power of our moral example, America is back," Obama said.
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