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.

Consider the different American views of recent bids for independence.

Chechnya? No.

East Timor? Yes.

Abkhazia? No.

South Sudan? Yes.

Palestine? It’s complicated.

It is an acutely delicate subject in the West, where Britain wants to keep Scotland and Spain wants to keep Catalonia. The United States, after all, was born in revolution, breaking away from London without consent of the national government — something that the Obama administration insists Crimea must have. The young American union later fought a civil war to keep the South from breaking away. Even today, there is occasional fringe talk of secession in Texas.

“No state has been consistent in its application of this,” said Samuel Charap, a Russia specialist at the International Institute for Strategic Studies. During a trip he took to Moscow last week, Mr. Charap said, Kosovo was the precedent cited repeatedly by Russians defending the Crimea intervention. “It’s like, ‘You guys do the same thing. You’re no better. You’re no different.’ ”

The Kremlin has likewise cited Scotland, which will soon vote on whether to remain in the United Kingdom, in recent days as another example. But American officials note that no foreign power sent troops into Edinburgh to replace its local government and stage a vote days later under the barrel of a gun. The Kremlin, they argue, is trying to legitimize an invasion and a land grab with false comparisons to situations like Kosovo.

“It’s apples and oranges,” said Benjamin J. Rhodes, President Obama’s deputy national security adviser. “You can’t ignore the context that this is taking place days after the violation of Ukrainian sovereignty and territorial integrity. It’s not a permissive environment for people to make up their own minds.”

While the concept of state sovereignty can be traced to the Treaty of Westphalia in 1648, the issue has been especially tricky for American presidents in the quarter century since the end of the Cold War. Ukraine itself is the product of a breakup, that of the Soviet Union, when 15 separate nations emerged from the wreckage. Several of those new nations then confronted their own separatist movements, notably Chechnya in Russia; Transnistria in Moldova; Abkhazia and South Ossetia in Georgia; and Nagorno-Karabakh in Azerbaijan.

Although Woodrow Wilson championed self-determination after World War I, the United States like most powers generally prefers stability and the status quo, so it has largely supported preserving borders where they are. During the first Russian war in Chechnya, Bill Clinton even likened Boris N. Yeltsin to Abraham Lincoln, a comparison many in Washington came to regret amid the carpet bombing of Grozny, the Chechen capital.

“Self-determination has been a controversial doctrine since Wilson, and hell to apply,” said Stephen Sestanovich, a former ambassador at large to the Soviet states and the author of a new book, “Maximalist,” on American foreign policy. “One consistent point: It can’t be used as a cudgel by big states to break up their neighbors. Russia’s own record here does not entitle it to the benefit of the doubt.”

Russia’s two ferocious wars in Chechnya since the 1990s were fought to prevent the very strain of separatism it now encourages in Crimea. In backing President Bashar al-Assad of Syria in his civil war against rebels, Russia argues that state sovereignty should not be violated, an argument it has turned on its head in Ukraine.

Of course, the fractiousness that has chopped up the Soviet empire into increasingly smaller and often dysfunctional pieces is not relegated only to that part of the world, although in the West in recent years it has played through political and legal processes rather than military ones.

In September, for example, Scotland will hold a referendum on secession, a vote being held with the acquiescence of London. In November, Catalonia plans its own vote on independence from Spain, although in that case the Madrid government has called it illegal. Quebec held unsuccessful referendums on independence from Canada in 1980 and 1995 and as recently as last week its separatist government was discussing whether another should be held.

But Kosovo is the case that deeply divided Europe. After Yugoslavia fell apart, the Kosovo Liberation Army, a rebel group representing the Albanian minority, struggled against the Serbian government, which responded with punishing force until Mr. Clinton intervened in 1999 with a 78-day NATO bombing campaign.

Kosovo declared independence in 2008. The United States under George W. Bush recognized it, as did Britain, France and Germany, but Russia adamantly rejected it, as did Spain. The International Court of Justice later ruled that Kosovo’s declaration was legal.

“We never saw it as setting a precedent, but there were some nations that saw it that way and still do,” said James W. Pardew, who was Mr. Clinton’s special representative for the Balkans.

John B. Bellinger III, who was the top lawyer at the State Department under Bush, said: “We were very careful to emphasize that Kosovo was a unique situation. We were fond of saying it was sui generis — and it did not create a precedent that would likely be replicable anywhere else.”

That is not how the Kremlin sees it. Ever since, Russia has cited Kosovo to justify support for pro-Moscow separatist republics in places like Georgia, where it went to war in 2008 and recognized the independence of Abkhazia and South Ossetia over Western objections.

“Kosovo is very much a legitimate precedent,” said Dimitri K. Simes, president of the Center for the National Interest, a Washington research organization, echoing Moscow’s argument. “Independence was accomplished despite strong opposition by a legitimate, democratic and basically Western-oriented government of Serbia.” By contrast, he said, the new pro-Western government in Kiev “lacks legitimacy,” since it came to power by toppling a democratically elected president.

The Obama administration maintains that the cases cannot be compared. Serbia, White House officials said, lost its legitimacy and right to rule in Kosovo by its violent crackdown. Despite Russian claims, there has been little, if any, independent evidence of such a campaign against the Russian-speaking population in Crimea.

“There’s no repression or crimes against humanity that the government in Kiev has committed against the people of Crimea,” Mr. Rhodes said. “There’s no loss of legitimacy.”