Biden says Putin's invasion of Ukraine shows he has 'much larger ambitions' and wants to 're-establish the former Soviet Union'

"I think that his ambitions are completely contrary to the place where the rest of the world has arrived," he added.

Biden also announced the deployment of an additional 7,000 US troops to Germany to support its allies in the North Atlantic Treaty Organization, but made clear that the US will not fight in Ukraine. However, if Putin were to advance into countries that are part of NATO, the US will get involved, he added.

NATO Secretary-General Jens Stoltenberg also vowed that the alliance will defend its territory should Russia attack a member country.

"The only thing I'm convinced of is if we don't stop now, he'll be emboldened," Biden said of Putin. "If we don't move against him now with these significant sanctions, he will be emboldened."

The president on Thursday announced a new round of harsher sanctions against Russia, building on the previous set of economic sanctions imposed on Tuesday. Biden met with G7 leaders and agreed upon further sanctions against Russia after troops moved in on Ukraine's northern, southern, and eastern borders early Thursday morning.

"We will limit Russia's ability to do business in dollars, euros, pounds and yen to be part of the global economy," Biden said. "We're going to stop the ability to finance and grow the Russian military. We're going to impair their ability to compete in a high-tech 21st-century economy."

In addition to Biden, several US lawmakers on both sides of the aisle, such as GOP Sen. Ted Cruz of Texas and Democratic Sen. Chris Coons of Delaware, have sounded the alarm on Putin wanting to expand Russia's borders. 

Putin over the years has repeatedly suggested that Ukraine is not a real country, and has said that Ukrainians and Russians are "one people." During an incendiary speech on Monday filled with falsehoods, Putin rewrote history and suggested Ukraine was "entirely created by Russia." 

The Russian president's aggression toward Ukraine is driven by a desire to reestablish Russia's supremacy in countries that were formerly part of the Soviet Union, experts say. 

Former US Secretary of State Madeleine Albright in a recent New York Times op-ed said that her first impression of Putin, a former KGB operative, was that he was "embarrassed by what happened to his country and determined to restore its greatness." Putin told Albright he hadn't expected the entire Soviet Union to collapse. 

Putin has for years complained about NATO's eastward expansion, presenting it as an existential threat to Russia. Along these lines, he's pushed for Ukraine to be permanently barred from NATO. The alliance and the US have made it clear that this is a non-starter. 

"The current crisis between Russia and Ukraine is a reckoning that has been 30 years in the making. It is about much more than Ukraine and its possible NATO membership. It is about the future of the European order crafted after the Soviet Union's collapse," Angela Stent, a senior fellow at the Brookings Institution and a former US national intelligence officer for Russia and Eurasia, recently wrote in Foreign Affairs. 

During his roughly two decades in power, Putin has dedicated much of his energy to challenging the post-Cold War security framework built by the US and its allies — vying to undermine it to Russia's advantage. The Russian leader's unprovoked invasion of Ukraine is the most audacious, and potentially catastrophic, manifestation of these ambitions to date.