Sen. Marco RubioMarco Antonio RubioTrump replaces McMaster with Bolton as national security adviser Orlando March for Our Lives protesters to march to Rubio's downtown office, Pulse nightclub Lawmakers eye crackdown on China’s Confucius Institutes MORE (R-Fla.) put a heavy emphasis on foreign policy and national security -- not immigration -- during in his speech at the annual Conservative Political Action Conference on Thursday.

Amid the ongoing crisis in the Ukraine, Rubio warned the crowd of the potential conflicts facing the nation and railed against President Obama’s foreign policy, pitching a more aggressive role for the United States in global conflicts.

Rubio said, that, with some changes, the U.S. is “on the verge of a new American century,” and charged that Democrats are standing in the way of such progress.

“This disunity they’ve created in our country is unacceptable and is holding us back from that American century,” he said of Democrats.

But Rubio said that the U.S. can overcome its economic challenges when Obama leaves office — more difficult to address will be the national security challenges facing the nation.

He ticked off a litany of conflicts and threats developing around the world, touching on China’s maritime expansion, the Venezuelan government’s aggression against its citizens, North Korea and Iran’s nuclear programs, the splintering of Al Qaeda across a dozen countries, and Russian President Vladimir Putin’s aggressive engagement in the Ukraine as concerns.

Rubio warned of a world in which “North Korea can blow up California” and “Iran can wipe Israel off the face of the Earth,” and framed the U.S. as the only possible answer to such conflicts.

“All the problems of the world, all the conflicts of the world are being created by totalitarian regimes,” he said. 

He added: “There is only one nation on earth capable of rallying and bringing together the free people on this planet to stand up to the spread of totalitarianism. There is only one nation on earth that can do that, and that is ours."

And he knocked Obama as “a president who believes that by the sheer force of his personality he will be able to shape global events,” and called for a more aggressive foreign policy, “deeply rooted in our values and in our moral principles.”

Rubio's focus on national security comes as he considers a potential run for president in 2016, when foreign policy is likely to take a central role in the debate, with Democrats expected to nominate former Secretary of State Hillary ClintonHillary Diane Rodham ClintonWhite House would like to see Biden ‘in the boxing ring’ in 2020 House Judiciary chair subpoenas DOJ for FBI documents The suit to make Electoral College more ‘fair’ could make it worse MORE.