Leftist Turks shout slogans during a protest outside the US embassy in Ankara, Turkey, after a US congressional committee approved a resolution branding the 1915 killing of Armenians a genocide. Photograph: Burhan Ozbilici/AP

When a committee of the US Congress foolishly voted last week to brand as genocide the 1915 slaughter of Armenians by Ottoman Turks, there was plenty of blame to go around. Ethnic lobbies, big-money politics and narrow-minded congressmen all played their part. Together they poked a gratuitous stick in the eye of a valuable friend. Once again America repeated its classic foreign policy blunder: do something that makes you feel good now, but that in the long run actually undermines American security interests.

Amid all this finger-pointing, however, it is only fair to single out one other culprit for this misguided vote: Turkey itself. After the vote, which was broadcast live on Turkish TV and followed as passionately if it were a World Cup match, thousands of Turks took to the streets in protest. They were right to be angry. As Turks try to figure out who brought this insult upon them, though, they should pause before a mirror.

Turkey has done three things that helped push the House foreign affairs committee toward its vote. First, despite signing a highly promising accord with Armenia last year, it has failed to close the deal. Relations between the two countries remain frozen, partly because of Turkey's insistence on tying normalisation to a withdrawal of Armenian troops from disputed Nagorno-Karabakh. The deal was to have included a clause assigning questions about the 1915 massacre to a committee of historians. If it had been signed and ratified, the genocide issue would be off the table – and probably off Washington's agenda.

Second, Turkey suffers from a creeping image deterioration in Washington. Some feel that Turkey has become too close to Iran, and resent the vigour of Turkey's opposition to sanctions on the Iranian regime – especially important since Turkey holds a rotating seat on the UN security council. These doubts might not have become as powerful if Israel, Turkey's old friend, had come to its rescue with lobbying help on Capitol Hill, as it has in the past. But Turkish leaders have sharpened their criticism of Israel lately, and the Israelis, seeking to show that they too have cards to play in this game, did not rush to help Turkey this time.

In considering not just the substance of its Middle East policy but the style in which it is presented, Turkey would do well to balance its relationships with Iran, Israel and the US more deftly.

Third and perhaps most profoundly, Turkey has brought itself to this point by its refusal to confront what happened to Ottoman Armenians in 1915. One reason Turks are so outraged at accusations made against their ancestors is that they have little access to the historical truth. Textbooks are distorted and politicians whip up nationalist fervor for votes. "Why are we trying to cover up this horrible crime, why are we trying to defend the murderers, to disguise their crimes, why are we squirming to keep truth buried, even at the risk of being humiliated?" the Turkish commentator Ahmet Altan asked in a column after the vote in Washington.

"If you feel humiliated, you should take a hard look at yourself and what you hide."

In the last few years, Turkey has emerged to play a new and highly promising role in the Middle East and beyond. As a successful Islamic democracy allied with the west, it can be a powerful force for regional peace – and, not incidentally, a uniquely valuable partner for the US. For Turkey to play the role it seeks as a broker and conciliator, though, it it must continue to mature politically and diplomatically. The vote in Washington should lead Turks to reflection. A final accord with Armenia, a more elegant way of balancing relations with Iran, Israel and the United States, and an end to denial of what happened in 1915 would dramatically improve both Turkey's global stature and its ability to help stabilise the world's most volatile region.