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French President Francois Hollande's decision to fly to Germany within hours of taking office Tuesday isn't just a sign of how deep Europe's troubles are -- it underlines the deep alliance that the former antagonists have developed over the decades since World War II.

Hollande follows predecessor Nicolas Sarkozy in traveling to Berlin on the day of his inauguration to meet Chancellor Angela Merkel.

And it isn't one-way traffic: Merkel, now on her third French president, headed for Paris -- and a meeting with Jacques Chirac -- on her first foreign trip the morning after being sworn in as Germany's leader in 2005.

Over the decades, France and Germany have come to view themselves as the motor of the European Union -- a duo without which the bloc would struggle to shape policy.

It's a tradition that goes back well beyond Merkel and Sarkozy, fellow conservatives who became so central to Europe's debt crisis response that they were frequently referred to as "Merkozy" -- and it has frequently crossed party lines.

Though Merkel's a conservative and Hollande's a socialist, people are already now talking about "Merkollande" in hope they will be able to bridge their differences.

That's also not without precedent.

Back in the 1970s, center-left West German Chancellor Helmut Schmidt worked closely together with center-right French President Valery Giscard d'Estaing.

Conservative Chancellor Helmut Kohl's good relationship with Socialist President Francois Mitterrand was reflected in a poignant gesture of reconciliation in 1984, in which they held hands during a ceremony at a World War I cemetery in Verdun, France. It was a friendship that helped ease the way to German reunification in 1990.

Merkel's center-left predecessor, Gerhard Schroeder, initially showed an interest in closer ties with Britain but bonded with the conservative Chirac over their shared opposition to the U.S.-led war in Iraq in 2003.

Germany and France have the 17-nation eurozone's biggest and second-biggest economies, respectively. Already, German officials are keen to talk up the chances of finding common ground with Hollande, who has criticized Merkel's austerity-led approach to the debt crisis and wants a greater emphasis on growth.

Peter Altmaier, the parliamentary chief whip of Merkel's conservative bloc, said Tuesday that "the German-French relationship has a high priority for us."

"We assume that Germany and France will continue in future to be the motor of European integration, and that we will together be the guarantors of stability and solidity in the eurozone," he said.