Ukraine, as the largest former Soviet republic in Europe besides Russia itself, has been a key part of alliance talks since it declared independence from the USSR in 1991. In the three decades since, NATO expansion has put four members on Ukraine's borders.

Russian military forces and Russian-backed separatists have invaded Ukraine. NATO Secretary-General Jens Stoltenberg says NATO allies condemn in “strongest possible terms” Russia’s “horrifying attack” on Ukraine. With the invasion, a 30-year-old foreign policy debate has made a return to center stage.

The question: Should NATO, the mutual defense pact formed in the wake of World War II that has long served to represent Western interests and counter Russia’s influence in Europe, expand eastward?

NATO’s founding articles declare that any European country that is able to meet the alliance’s criteria for membership can join. This includes Ukraine. The U.S. and its allies in Europe have repeatedly said they are committed to that “open-door” policy.

But in the words of Russian President Vladimir Putin, NATO’s eastward march represents decades of broken promises from the West to Moscow.

“You promised us in the 1990s that [NATO] would not move an inch to the East. You cheated us shamelessly,” Putin said at a news conference in December.

The U.S. says a ban on expansion was never on the table. But Russia insists it was — and now, Putin is demanding a permanent ban on Ukraine from joining the pact.

“Unsurprisingly, when you look at the evidence, what happened is somewhere in between,” said Mary Sarotte, a post-Cold War historian whose book about those negotiations, Not One Inch: America, Russia, and the Making of Post-Cold War Stalemate, was published last fall.

Stay up to date with us

Subscribe

Get weekly Canon roundups straight to your inbox