WE WERE among those who doubted that a meeting on Ukraine in Geneva Thursday could produce results, given the weak Western response to Russian aggression. So count us as pleasantly surprised by the “initial concrete steps to de-escalate tensions and restore security” that the parties announced. The accord calls for the Russian-backed groups that have taken over government buildings in eastern Ukrainian cities to evacuate and disarm under the watch of international monitors. In exchange, Ukraine’s government committed to constitutional reforms giving eastern regions more autonomy, and the United States and Europe will hold off on further sanctions against Russia.

The deal promises to arrest what had looked like an accelerating slide into anarchy or even civil war in eastern Ukraine. As Secretary of State John F. Kerry pointed out, so far it exists merely as “words on paper,” and it remains to be seen whether Russia will fully unwind the quasi-covert offensive it launched 10 days ago. Mr. Kerry and President Obama suggested that if Western governments do not see progress by early next week they will go forward with new sanctions; it will be important to stick to that deadline.

“De-escalation” does not mean that Vladi­mir Putin has given up his goal of bringing as much of Ukraine as possible under Moscow’s suzerainty — and making the rest ungovernable. His performance in a televised appearance Thursday, in which he reiterated that the Russian parliament had given him authority to invade eastern Ukraine and referred to the region as “new Russia,” made clear that his ambition to upend the post-Cold War order in Europe remains unchecked.

Moscow is still demanding constitutional changes that would make the eastern regions virtually independent and give them a veto over national policies. Mr. Kerry said that Foreign Minister Sergei Lavrov indicated that the Russian troops still massed on Ukraine’s borders would be drawn down only “as the constitutional process unfolds.” In other words, Moscow reserves the right to use force if it does not get the chopped-up Ukraine it wants.

Ukraine’s government has promised decentralizing reforms. But any new political order that satisfies the imperative of an independent nation capable of making its own decisions about economic relationships and alliances will not be acceptable to Mr. Putin. If he slows his creeping invasion of Ukraine, it must be seen as a tactical maneuver. The Russian ruler is avoiding Western sanctions that might have targeted more members of his inner circle while giving Ukraine’s government the chance to give in to his demands. He appears to hope that the Obama administration and European Union will lean on Kiev to comply. “The U.S. authorities have assured us,” said Mr. Lavrov, “that the constitutional reform will take place.”

All those concerns notwithstanding, Mr. Kerry was justified in calling the Geneva accord “a good day’s work.” If it is implemented, Ukraine could be diverted from a downward spiral that could have led to civil war. The United States and its allies must now ensure that Russia genuinely puts an end to its intervention — and that Ukraine is not forced into unacceptable concessions in order to prevent another one.