In their Dec. 7 op-ed, “A win for Russia, Ukraine and the West ,” Michael O’Hanlon and Jeremy Shapiro ignored the motivation for Russian President Vladi­mir Putin’s aggression: He realizes that he cannot cure Russia’s domestic problems, so he must appeal to nationalism and the belief in a “Greater Russia.”

Mr. Putin thought high oil prices and disarray in the European Union would help his aggression succeed. But with oil prices falling, increasing his domestic problems, he will undoubtedly seek to use the appeal of Greater Russia. We live in a dangerous moment. If Mr. Putin were overthrown, perhaps someone like him or worse would take his place.

The authors wrote, “Long-term Russian weakness means that the West can afford to compromise now.” No, long-term Russian weakness is the threat because it motivates Russian leaders to take the path of aggression. We must demonstrate our resolve to defeat that aggression while recognizing that certain Russian “gains” such as Crimea cannot be reversed. A 21st-century policy of containment is needed. The 20th-century one succeeded.

Frank A. Nicolai, Fort Washington

Michael O’Hanlon and Jeremy Shapiro join former secretary of state Henry Kissinger and former national security adviser Zbigniew Brzezinski in advocating that the West appease Russia. They suggest Ukraine give up its sovereign right to choose its economic and security associations in return for Russia committing to respect Ukrainian territorial integrity as it promised to do in 1994 and has now shamelessly and unapologetically not done with the invasion and illegal annexation of Crimea last spring.

As sanctions bite ever more painfully in Russia, inflation rises, oil prices fall and the mothers of soldiers killed in Ukraine grieve, President Vladi­mir Putin’s support is falling among the Russian people. Now is not the time for appeasement. Now is the time to support Ukraine’s struggle for sovereignty, dignity and independence.

William Taylor, Arlington

The writer, U.S. ambassador to Ukraine from 2006 to 2009, is acting president at the U.S. Institute of Peace.

Michael O’Hanlon and Jeremy Shapiro’s proposal would make a bad situation much worse.

Their suggestion to hold a referendum in Crimea after nearly a year of suppression of those opposing Russian annexation and oppression of minority Ukrainians and Tatars is risible. They claimed that NATO “has expanded right up to Russia’s borders since the Cold War.” For decades NATO members Norway and Turkey bordered the Soviet Union. Their advocacy of a pan-European security body superior to NATO even goes beyond then-Russian President Dmitry Medvedev’s discredited 2008 project.

Most alarming is their inability to grasp the nexus between President Vladi­mir Putin’s kleptocratic authoritarianism and his aggressive foreign policy. Weakening NATO, the guarantor of European democracy, in a naive attempt to propitiate him would only invite further adventurism and destabilize an area of more than 100 million people whose 12 countries joined NATO since the Cold War precisely for protection against Russia. The 20th century should have made clear that great powers making deals over the heads of smaller nations is morally bankrupt and politically disastrous.

Mike Haltzel, Alexandria

The writer was Democratic staff director of the Subcommittee on European Affairs of the Senate Foreign Relations Committee from 1994 to 2005.