The newest wave of separatism in eastern Ukraine feels very familiar. In the last few days, protesters waving Russian flags have seized government buildings by force, barricaded themselves inside, declared their intention to break away from Ukraine and appealed to Russia to send in troops to protect them. At every step, they followed the script that ended last month with the Russian annexation of Crimea. But the stage this time didn’t seem to fit the performance.

Eastern Ukraine is not like Crimea. It is far bigger, more diverse, better integrated into Ukraine’s economy and more vital to its survival than Crimea, and if the action proceeds again toward a Russian invasion of these territories, the Kremlin’s choreographers will have a much harder time pulling it off. The stakes this time are incomparably higher.

For one thing, Ukraine will defend itself. In February, when pro-Russian gunmen seized the Crimean parliament and installed a separatist leader, Ukraine did not have a central government capable of stopping them. The revolutionaries in Kiev, the capital, had only toppled the old regime a week before, and they were too busy deciding who would lead the nation to mount any defense of Crimea. The picture since then has changed. Ukraine’s institutions are functioning, and though the country’s economic affairs are hardly in order, it does have a police force and a military command structure to throw into the fight.

On Monday, Ukraine’s acting President, Oleksandr Turchinov, made clear that Ukraine would not sit by as it did with Crimea and watch another Russian land grab. “This is the second wave of the Russian Federation’s special operation against Ukraine,” he said in a televised address to the nation. “Its goal is to destabilize the state and overthrow Ukrainian power, disrupt the elections and tear our country into pieces.” By then, his security chiefs had already raced to eastern Ukraine to prepare a defense of its cities. Police had begun arresting separatists across the region and fighting to take back occupied buildings in what they termed a “counterterrorism operation.” Ukraine’s parliament then passed tougher laws on Tuesday against separatism, but stopped short of a proposed state of emergency in three eastern regions – Donetsk, Luhansk and Kharkiv – where Ukrainian fighter jets had begun to patrol the skies.

Considering that only a few thousand protesters took part in the pro-Russian demonstrations over the weekend, the reaction seemed extreme. But the risks were high enough to warrant such measures. Eastern Ukraine, particularly the coal-mining region known as the Donets Basin, or Donbass, is the most densely populated and economically important part of the country. Donetsk alone accounts for 12% of Ukraine’s economy, more than any other region except the capital.

The demographics of eastern Ukraine also would not lend themselves to a secessionist referendum. According to the most recent census held in 2001, ethnic Ukrainians make up nearly 60% of the population in Donetsk and Luhansk, and more than 70% in Kharkiv, compared to only 24% in Crimea, where the majority are ethnic Russians. So it is hardly likely that a referendum in these eastern regions would result in a decision to break from Ukraine and join Russia, at least not by the overwhelming majority that was seen in Crimea last month.

More importantly, such a referendum could only be held if Russia first manages to occupy these regions, kick out the Ukrainian security forces and install a separatist government that could push ahead with a Crimean-style plebiscite under the gun. That would mean a Russian land invasion and, most likely, the start of a full-scale war that would cost many lives on both sides, pitting the armies of two fraternal nations against each other, nations that share ties of culture, religion, language and oftentimes blood.

Though Russia would surely win such a conflict, the conquered territory of east Ukraine would be much harder to defend. Whereas the Crimean peninsula could be sealed off with only two Russian military checkpoints – one on each of the roads leading to mainland Ukraine – a Russian conquest of any eastern region would create a wide-open military front thousands of kilometers long. Holding that line would stretch Russia’s armed forces to their limits.

On top of that, the diplomatic excuses Russia offered for conquering Crimea would seem very thin if applied to Ukraine today. In March, as it set the stage for its annexation of Crimea, Russia played up the threat from right-wing militants involved in Ukraine’s revolution this year. But those militant groups, namely the ultranationalist party Right Sector, have faced a crackdown from Ukraine’s new government, and they are actively being disarmed. So any claims that ethnic Russians in Ukraine are under threat from some kind of “fascist” force would be even flimsier than they were a month ago.

But none of that means Russia lacks the stomach or the will for another incursion. Vyacheslav Nikonov, a prominent member of the ruling party in Russia, said on Monday that violence against the separatists in eastern Ukraine could provoke an invasion. “If the government in Kiev moves in its troops or uses special forces, that could lead to an even bigger explosion and to Russian intervention,” he told Russia’s RIA Novosti news agency. The following morning, Russia’s Foreign Ministry claimed that Kiev was not only sending troops to eastern Ukraine but using American military contractors who were working in tandem with Right Sector thugs. “They have the goal of crushing the residents in the southeast of the country who have come out to protest the policies of the current government in Kiev,” the Ministry’s statement said.

That would likely be enough of an excuse for Russia to proceed with an intervention, which would not take long to organize.

Since February, Russia has been amassing tens of thousands of troops along its border with Ukraine, and Western military leaders have warned that these armies are poised for an attack. “This is a very large and very capable and very ready force,” U.S. Air Force General Philip Breedlove, NATO’s supreme allied commander in Europe, told reporters last week. “We think it is ready to go and we think it could accomplish its objectives in between three and five days if directed to make the actions.”

All of that presents a tempting opportunity for Russia. The prize of eastern Ukraine would come with its vast reserves of natural resources, particularly metals and coal, and its conquest would cripple Ukraine’s new pro-Western government, whose downfall Russia sees as a valuable end in itself. Judging by recent opinion polls, an invasion of eastern Ukraine could also prove popular among the Russian public. In early March, when Russia had just occupied Crimea, 65% of respondents in a national poll agreed with the following statement: “Crimea and the eastern regions of Ukraine are in essence Russian territory, and Russia has the right to use military force to defend their populations.” In the same survey, which was conducted by the independent Levada Center polling agency, 79% of respondents said that Russia should annex any region of Ukraine that supports such a move in a referendum.

So what about the costs? In diplomatic terms, Russia could probably bear them, as it has little left to lose. The Kremlin has already crossed a threshold toward isolation from the West by annexing Crimea, and it’s not clear how much further the West could or would go in punishing Russia for another land grab. As President Obama has made clear, the United States. will not go to war with Russia over Ukraine. “I think even the Ukrainians would acknowledge that for us to engage Russia military would not be appropriate, and wouldn’t be good for Ukraine either,” Obama told NBC last month. “What we are going to do is mobilize all of our diplomatic resources to make sure that we’ve got a strong international coalition that sends a clear message.”

In the coming days, as Ukraine scrambles to stamp out the separatist forces in its eastern regions, Russia will have to decide whether to heed that message or go on the march. But its decision will not be swayed one way or another by the threats from Obama’s international coalition, as Western sanctions have so far only hardened the resolve of the Kremlin elites around President Vladimir Putin. In the end, Putin’s decision to invade eastern Ukraine will come down to a cold calculation of the risks and gains. Both militarily and economically, the risks are far greater for Russia than they were in Crimea – but so are the potential gains.

Contact us at letters@time.com.