Rügen is best known as a popular German tourist destination. But now the Baltic Sea island has taken on a new role as staging point for an energy project that is as ambitious as it is controversial: the Nord Stream gas pipeline from Russia to Germany.

Next spring the first pipeline segments will likely be dropped to the sea floor in a line that will wind through Russian, Finish, Swedish, Danish and German waters—conspicuously avoiding the Baltic states and Poland.

This is because the Nord Stream project is part of an exclusionary agreement between Moscow and Berlin—nicknamed in circumvented Warsaw the “Molotov-Ribbentrop Pact,” after the 1939 Soviet-Nazi deal to carve up Poland. It would have been much cheaper to build an overland pipeline through Eastern Europe, but the purpose of Nord Stream from the beginning was to bypass countries Moscow still considers to be part of its sphere of influence.

Russia’s geopolitical message here is clear: It doesn’t trust the new EU member states as transit countries or even as energy consumers and is willing to incur enormous costs to bypass them. The other message—or implied threat—is that Nord Stream will allow the Kremlin to cut off gas deliveries to Eastern Europe through current pipelines without reducing energy supplies to Germany. But what sort of message does Germany, a fellow EU member, intend to send to its neighbors?

Nord Stream was championed by former German Chancellor Gerhard Schröder, who now serves as one of its executives. From within her previous coalition government, current Chancellor Angela Merkel lobbied successfully for EU endorsement of the project even though the pipeline consortium is registered in Switzerland and controlled by Russia’s Gazprom. Of the dozens of companies involved in the pipeline’s construction, not one is from the Baltics, Central or Eastern Europe.

Germany’s recent election results produced a ripple of hope among the countries on Russia’s periphery. With the traditionally pro-Moscow Social Democratic Party out of the governing coalition, would Mrs. Merkel perhaps seek to change the terms of the Nord Stream agreement and push Russia to alter the route so that the pipeline would cross the waters or territories of Eastern EU members? Perhaps she would lobby Moscow to include also East European companies in the Nord Stream consortium? At least, it was hoped, Berlin would throw its weight behind the Nabucco pipeline, which seeks to improve Central and Eastern Europe’s energy security with the help of Caspian and Middle Eastern gas. After all, Germany’s RWE is part of the Nabucco consortium and Mr. Schröder’s pro-EU former foreign minister, Joschka Fischer, is now a lobbyist for the project.

Recent progress on Nord Stream, however, has dashed those hopes. The Nordic countries had until now delayed the project’s approval, raising environmental concerns, which most interpreted as unease about the pipeline’s geopolitical implications. Last Thursday, though, Finland and Sweden—which holds the European Union presidency until the end of the year—joined Denmark in signing off on the project. It is this political momentum that has spurred the rush to get pipeline segments out to Rügen and other staging points. The very realistic prospect that construction on Moscow’s pet project might begin early next year is a symbolic blow to those seeking to reduce Europe’s energy dependence on Russian gas. Most of all, it is a blow to any semblance of EU unity on energy security. Russia’s neighbors, both within and without the EU, are already reeling from a sense of Euro-Atlantic abandonment following Washington’s “reset” policy toward Russia and the EU’s lackluster outreach to its Eastern neighbors.

It would be unrealistic to expect Berlin to change tack on Nord Stream so late in the game. But a newly re-elected Angela Merkal should carefully consider the foreign policy messages that come with laying pipe on the Baltic Sea floor.

In order to reassure fellow EU members and the institution as a whole, Berlin would do well to support what the European Commission considers its “strategic priority”: The so-called Southern Corridor, which includes Nabucco and several smaller pipeline projects. As a European heavyweight, Germany’s mere rhetorical and diplomatic support would go a long way in encouraging EU energy unity. Most importantly, it would send the message to Moscow that its “divide and conquer” energy policy has its limits.

Alexandros Petersen is Dinu Patriciu Fellow for Transatlantic Energy Security and associate director of the Eurasia Energy Center at the Atlantic Council.  This essay was previously published as “The Molotov-Ribbentrop Pipeline” in the Wall Street Journal