"This is the beginning of a summer of discontent."
The proximate cause of the protest was a plan to demolish a park, but it may also mark a belated Turkish Spring as protesters strive to confront the relentless rule of the Islamist AKP, which is supported by the EU and Obama.
The official opposition has failed to stop the AKP's takeover of the country and the press and other elements of the government have been locked up by Erdogan on the pretext that they engaged in a vast conspiracy of thousands against his rule. Turkey has tens of thousands of political prisoners and represses its ethnic minorities, but despite all that Western political interests support Erdogan because of his economic policies.
But the latest violence calls attention to the habitual brutalities of the AKP regime under Erdogan.
Broken glass and rocks were strewn across a main shopping street. A group of primary school children ran crying from the tear gas while tourists caught by surprise scurried to get back to luxury hotels lining the square.
"We do not have a government, we have Tayyip Erdogan...Even AK Party supporters are saying they have lost their mind, they are not listening to us," said Koray Caliskan, a political scientist at Bosphorus University who attended the protest. "This is the beginning of a summer of discontent."
Riot police clashed with tens of thousands of May Day protesters in Istanbul weeks ago. There have also been protests against the government's stance on the conflict in neighbouring Syria, a recent tightening of restrictions on alcohol sales and warnings against public displays of affection.
"This isn't just about trees anymore, it's about all of the pressure we're under from this government. We're fed up, we don't like the direction the country is headed in," said 18-year-old student Mert Burge, who came to support the protesters after reading on Twitter about the police use of tear gas.
"We will stay here tonight and sleep on the street if we have to," he said.
The Islamist AKP regime is working to outlaw alcohol, supposedly for public safety reasons, but in reality for religious ones. And as Erdogan begins turning Turkey into Iran, he may begin facing the same protests that Ahmadinejad did.