Sam Rainsy (center, R), president of the opposition Cambodian National Rescue Party (CNRP) and party vice-president Kem Sokha (center, L), stand on a vehicle as they lead a protest in Phnom Penh December 29, 2013.

Nicolas Axelrod/Getty Images
Protesters in the Cambodian capital included Buddhist monks, garment workers, farmers and supporters of the main opposition party.
PHNOM PENH, Cambodia — Tens of thousands of antigovernment demonstrators marched through Phnom Penh on Sunday in one of the biggest acts of defiance against the nearly three decades of rule by Cambodia’s authoritarian prime minister, Hun Sen.
The procession, which was peaceful and stretched for several miles through a commercial district of Phnom Penh, the capital, brought together protesters with a diverse list of grievances: Buddhist monks, garment workers, farmers and supporters of the main opposition party.
They were united in their calls for Mr. Hun Sen to step down, their chants — “Hun Sen! Get Out!” — echoing down the broad avenue where they marched.
In July, Mr. Hun Sen’s party claimed victory in disputed elections that the opposition and many independent monitoring organizations said were deeply flawed. Mr. Hun Sen formed a government despite the growing protests by the opposition, which has boycotted Parliament and is calling for new elections.
Cambodia’s political stalemate and protest movement have been somewhat overshadowed by the turmoil in nearby Thailand, where antigovernment demonstrators are rallying to block elections and install a “people’s council” to govern the country during what they describe as a hiatus from democracy.
But some analysts in Cambodia describe the past few months here as a watershed for Cambodian society, which for years has been dominated by the highly personalized rule of Mr. Hun Sen, whose party has tight control over major institutions in the country, including the army, the police, the judiciary and much of the news media.
Protesters blocking traffic and marching through downtown Phnom Penh remain a jarring sight after years during which the main message from the government has been that people should be grateful for the unity and development that Mr. Hun Sen brought to Cambodia after many years of war.
“It seems like a turning point in the history of civil society,” said Yeng Virak, the executive director of the Community Legal Education Center, a Cambodian human rights organization. “People feel more free to join protests and to identify themselves as part of the opposition.”