Russian President Vladimir Putin has announced he will suspend Russia‘s participation in the Treaty on Conventional Armed Forces in Europe in 150 days. This will allow Russia to deploy tanks and other heavy weaponry on its border with Europe for the first time since the end of the Cold War.

President Putin first indicated he might suspend the agreement, commonly known as the cfe Treaty, on April 26 in a State of the Nation speech to parliament. He directly linked the possibility to a U.S. plan to install a missile shield in Central Europe.

In his official announcement, however, Putin focused on other factors: nato countries have not ratified the updated version of the treaty created in 1999.

After the Soviet Union broke apart, the original cfe treaty became outdated. nato countries, including the U.S., have refused to ratify the treaty unless Russia complies with the Istanbul Agreements, a 1999 set of agreements where Moscow agreed to withdraw all troops from Georgia and Moldova. The Istanbul Agreements were signed concurrently with the updated cfe Treaty. Moscow claims the agreements are an entirely separate legal agreement from the treaty, but Western nations insist the Istanbul Agreements were part of the overall framework, and for Russia to ignore its obligations violates the spirit of the negotiations.

Former Russian President Mikhail Gorbachev, who signed the original treaty, agreed with Putin’s decision. “It would be utterly incomprehensible if Russia were the only country to follow the treaty, and the other side hadn’t even ratified it,” he said.

The announcement also cited U.S. plans to deploy forces in Bulgaria and Romania. But both U.S. and European leaders know that the announcement’s reference to “exceptional circumstances affecting the security of the Russian Federation and requiring immediate action” really refers to plans for a missile shield in Europe.

The historical importance of the treaty and the political weight of its suspension is troubling. The cfe Treaty was originally signed on November 19, 1990, and was considered a major contributing cause for the end of the Cold War.

There is no sign that the U.S. and Russia will reach an agreement. U.S. military experts consider a Russian proposal to co-host the missile shield’s radar system in Azerbaijan unworkable; even the Russians say it would not be complete until 2020.

No one knows what Moscow is planning after pulling out of the treaty. Russia is not necessarily looking for a massive deployment on the European border, but it does plan to disallow inspections once the 150-day period has passed. In addition, if Putin does not get his intended response to this latest act of bravado, he may pull Russia out of the Intermediate-Range Nuclear Forces Treaty, allowing Moscow to point nuclear weapons at Europe.

As Russia regresses to Cold War politics under its ex-kgb president, a German-led Europe—not the U.S.—will formulate a response. For more information about the past and future history between Europe and Russia, read “Russo-German Pact Imminent.”