Mr Erdogan declared that friendship with Armenia was no longer possible unless it withdrew from Nagorno-Karabakh.
Russia argues that Turkish-Armenian relations should not be linked to Nagorno-Karabakh, a view shared in Washington.
One thing is certain: making peace in Nagorno-Karabakh requires the skill of walking over a minefield.
Meanwhile, the ten-year ceasefire in the war over the disputed enclave of Nagorno-Karabakh is under strain.
Relations between the two were disrupted 16 years ago over Armenia's occupation of Nagorno-Karabakh, an enclave in Azerbaijan.
Nagorno-Karabakh, the much-disputed mountain enclave in western Azerbaijan, is full of Christian Armenians.
Yet Sadakhlo cannot last for ever, since it is an anomaly created by the geography of the Nagorno-Karabakh dispute.
Moldova and Azerbaijan, for example, have headaches with similar entities, Transdniestria and Nagorno-Karabakh.
In the end, all this pent-up trade depends on settling the Nagorno-Karabakh dispute.
This was sealed by Turkey in 1993 to show solidarity with Azerbaijan, which had just lost 20% of its territory, including Nagorno-Karabakh.
Too bad an ongoing conflict with neighboring Azerbaijan over the primarily Armenian region of Nagorno-Karabakh has turned off a big trade partner, Turkey.
Azerbaijan fought a war with neighbouring Armenia in the 1990s, in which it lost the Nagorno-Karabakh region, and the two sides may yet fight another.
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Indeed, absent Russian efforts to reduce tensions, Armenia and Azerbaijan would almost certainly have gone to war over Nagorno-Karabakh sometime over the past five or six years.
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The country has found it difficult to escape from poverty, partly because of a trade blockade imposed by neighbouring Turkey and Azerbaijan since the 1990s war with Azerbaijan over Nagorno-Karabakh.
In a dramatic shift, Turkey even dropped its long-running precondition that Armenia must withdraw from the territories that it occupied in the 1990s after its war with Azerbaijan over the mainly Armenian enclave of Nagorno-Karabakh.
Mr Gul's decision to accept an invitation from Armenia's president, Serzh Sarkisian, has raised expectations that Turkey may establish diplomatic ties and open the border it closed during the 1990s fighting between Armenia and Azerbaijan over Nagorno-Karabakh.
Unlike chess-players, though, all the participants can win in this game, it is hoped, if they agree on a common aim: peace between Turkey and Armenia, which would help to thaw the frozen conflict between Armenia and Azerbaijan over the (mainly Armenian) territory of Nagorno-Karabakh.
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