In a sweeping speech to a European audience in Brussels Wednesday, President Obama argued that the U.S. and Europe must stand together to stop Russia from undoing nearly a centuries' worth of democratic gains with its annexation of the Crimean peninsula.

The speech at the Palais Des Beaux Arts came in the middle of the president's weeklong trip across the Atlantic that has turned into a crisis response meeting for world leaders. Despite sanctions from both the U.S. and European Union against top Russian officials, Russian President Vladimir Putin has stood firm in his decision to incorporate Crimea as part of his country despite protestations from the international community that the referendum in which it split with Ukraine was illegal.

Mr. Obama traced the evolution of Europe through the 20th century and the Cold War as it shook off "an older, more traditional view of power." He argued that the Cold War was won not with military might, but because the values and ideals of the West inspired revolutions in Hungary, the Czech Republic, and East Berlin. Despite years of peace and prosperity - the only life that the younger generation of Europeans have known, he said - the international community is being "confronted with the belief that bigger nations can bully smaller ones to get their way - that recycled maxim that might makes right."

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"I come here today to insist that we must never take for granted the progress that has been won here in Europe, and advanced around the world. Because the contest of ideas continues for your generation," Mr. Obama said. "That is what's at stake in Ukraine today. Russia's leadership is challenging truths that only a few weeks ago seemed self-evident: that in the 21st century, the borders of Europe cannot be redrawn with force; that international law matters; and that people and nations can make their own decisions about their future."

Though the president called the current standoff over Ukraine a "moment of testing" for the U.S. and Europe, he was also clear that it is not the start of another Cold War. He noted that with a narrow definition of national interests or a more "cold-hearted calculus," the U.S. could "look the other way" because it has no close economic ties with Ukraine or shared borders threatened by a possible Russian annexation.

"But that kind of casual indifference would ignore the lessons that are written in the cemeteries of this continent. It would allow the old way of doing things to gain a foothold in this young century. And that message would be heard - not just in Europe -but in Asia and the Americas; in Africa and the Middle East," the president said.

He spent several minutes rebutting the various Russian arguments for the incursion, including a claim that ethnic Russians were being threatened. Rejecting Putin's use of Kosovo as a precedent for his actions, Mr. Obama noted that NATO only intervened after people had been systematically brutalized and killed for years, and that its separation from Serbia was done through a referendum in cooperation with the United Nations and neighbor countries. "None of that even came close to happening in Crimea," he said.

He also rejected claims that Americans were acting hypocritically because it invaded Iraq just a decade earlier - an invasion that Mr. Obama opposed, which bolstered his 2008 presidential campaign.

"America sought to work within the international system. We did not claim or annex Iraq's territory, we did not grab its resources for our own gain. Instead, we ended our war and left Iraq to its people and a fully sovereign Iraqi state could make decisions about its own future," he said.

"Neither the United States, nor Europe, has any interest in controlling Ukraine," he said, but rather want to ensure the Ukrainian people can make their own decisions. And the president dismissed as "absurd" the suggestion that America was conspiring with fascists in Ukraine or disrespecting the Russian people.

"The world has an interest in a strong and responsible Russia, not a weak one. And we want the Russian people to live in security, prosperity, and dignity like everyone else - proud of their own history," Mr. Obama said. "But that does not mean that Russia can run roughshod over its neighbors. Just because Russia has a deep history with Ukraine does not mean it should be able to dictate Ukraine's future."

Part of his task in the speech was to build more support for the possibility of future sanctions against key sectors of Russia's economy, which would undoubtedly cause more hardship for European nations that have closer trade relationships with Russia and are heavily reliant on its oil and gas. In a press conference with European leaders earlier Wednesday, Mr. Obama urged Europeans to take steps to diversify and develop their own energy sources to ensure their own security.

He also expressed concern about the diminished levels of defense spending among some member nations of NATO, which he identified as a key factor in maintaining international stability.

"Going forward, every NATO member state must step up and carry its share of the burden - by showing the political will to invest in our collective defense, and by developing the capabilities to serve as a source of international peace and security," he said in Brussels.

Further action by the U.S. and Europe could become necessary any day now. CBS News' David Martin reports that intelligence analysts increasingly believe Putin might send troops further into Ukraine to secure a corridor to Crimea, which would require seizing the cities of Kharkiv, Donetsk and Lehansk.