WASHINGTON — They wanted to break away from a country they considered hostile. The central government cried foul, calling it a violation of international law. But with the help of a powerful foreign military, they succeeded in severing ties.

The Kosovars’ secession from Serbia in 1999 drove a deep wedge between the United States and Russia that soured relations for years. Washington supported Kosovo’s bid for independence, culminating in 2008, while Moscow saw it as an infringement of Serbia’s sovereignty.

Now 15 years later, the former Cold War rivals again find themselves at odds, but this time they have effectively switched sides: Russia loudly proclaims Crimea’s right to break off from Ukraine while the United States calls it illegitimate. The showdown in Ukraine has revived a centuries-old debate over the right of self-determination versus the territorial integrity of nation-states.

The clash in Crimea is hardly an exact parallel of the Kosovo episode, especially with Russian troops occupying the peninsula as it calls a March 16 referendum to dissolve ties with Ukraine and rejoin Russia. Though the United States intervened militarily in Kosovo, it did not do so to take the territory for itself. But the current case underscores once again that for all of the articulation of grand principles, the acceptability of regions breaking away often depends on the circumstances.