The fall of the Berlin Wall remains one of the most iconic moments of the 20th century. For nearly 30 years, the wall represented the great divide between communism and democracy. On Nov. 9, 1989, the announcement that East Germans could travel to West Germany set into motion the wall’s demolition. By 1991, the Soviet Union had collapsed, and the Cold War was over.

The road to democracy has not been easy for many post-communist republics, where corruption and authoritarianism are still a threat to freedoms. But the end of Soviet rule ushered in momentous reforms – reshaping political systems, promoting free markets, and giving once-oppressed people a voice in their future. Had it not been for the extraordinary leadership and courage of Ronald Reagan, Margaret Thatcher, and Pope John Paul II, the world might look very different today.

Moscow’s Power Grabs

Russia’s aggression in recent years has led many to believe that the Kremlin is trying to rebuild the Soviet empire. Domestically, President Vladimir Putin has overseen an increasingly repressive and undemocratic regime, where opposition groups are punished and human rights are ignored. On the world stage, he has twice defied the sovereignty of neighboring states, invading Georgia in 2008 and Ukraine earlier this year. Accompanied by sharp anti-American rhetoric, the power grabs have seriously strained Moscow’s already fragile relations with the West.

Obama’s Failed ‘Reset’

It is disappointing that President Obama’s misguided concessions and promises have helped enable Putin’s ambitions. In 2009, he and then-Secretary of State Hillary Clinton pursued a fruitless “reset” in bilateral relations despite warnings that Russia could not be trusted to keep its commitments. Over the past five years, tensions between Russia and the United States have escalated rather than improved. Putin has spared no opportunity to rebuke America – either by defending the brutal regime of Bashar al-Assad in Syria or harboring U.S. fugitive Edward Snowden.

Earlier this year, Obama Administration officials confirmed that Russia had violated the Intermediate-Range Nuclear Forces Treaty, a pivotal Cold War pact signed by President Reagan and Soviet leader Mikhail Gorbachev to limit both countries’ arsenals. Officials say Russia’s illegal testing of prohibited missiles began as early as 2008, making the President’s later “reset” and push for a New START Treaty look ill-advised and naïve at best.

I have raised concerns about the Administration’s knowledge of Russia’s potential treaty violations, asserting that Congress should be made aware of this information when debating arms control treaties like New START. Along with Sen. Kelly Ayotte (R-N.H.), I offered an amendment to the National Defense Authorization Act that would require the Department of Defense to inform Congress about any significant cases of foreign noncompliance.

Ukraine Looks to the West

Russia’s military intervention in Ukraine and illegal annexation of Crimea are the latest in a litany of bold moves that America and our NATO allies cannot ignore. Political leadership and willpower – like that of Reagan and Thatcher – are necessary to hold strongmen like Putin accountable and defend liberty in the world. At the least, the United States and our allies should provide Ukraine with the arms and supplies to defend against Russian aggression. Russia may object to the eastward expansion of NATO’s influence into former Soviet satellites, but its encroachment has also reinvigorated the cause of freedom. Ukraine’s parliamentary elections this month, for example, resulted in overwhelming wins for pro-Western parties. Twenty-five years after the fall of the Berlin Wall, the strength of democracy continues to endure.