Keeping the peace: Mexican protesters say non-violence is key to change (+video) Mexico City - Demonstrators snaked across Mexico City last night along three separate routes, meeting in the historic Zócalo Plaza to protest the Sept. 26 disappearance - and likely massacre - of 43 teaching students nearly two months ago. It was billed as a peaceful march, with thousands of demonstrators ranging from families of the disappeared to university students and teachers, unionists and concerned citizens, calling for government action and justice. But clashes between some protesters and police led security forces in riot gear to clear the Zócalo later in the night. Earlier in the day a few hundred protesters attempting to shut down the Mexico City airport threw Molotov cocktails and rocks. As political energy continues to build nationally around the attack on students - an incident in which government officials, police, and drug cartels are implicated - many say keeping demonstrations peaceful is the key to meaningful change. "The situation is delicate enough that the climate of violence and the escalation of violent acts, they only benefit radical groups - and in some ways they benefit the government," says Erubiel Tirado, a national security expert at the Iberoamerican University in Mexico City. The state did it? On Thursday, protesters in Mexico City marched in an on-and-off light rain, chanting for President Enrique Peña Nieto to step down and shouting a refrain splashed across the city the past several weeks: "Fue el estado," or, "It was the state." Mexican flags painted black waved in the streets, and one seven-year-old girl holding her mother's hand carried a sign that read, "Am I next?" The case of the missing students has been the biggest challenge of President Peña Neito's two years in office. Protests took place across the country last night, with messages of solidarity coming in from activists across the world, including Paraguay, the Dominican Republic, the United States, and Germany. Relatives of the disappeared marched in three separate groups toward Mexico City in the days ahead of Thursday's protest. Many carried photos of their loved ones and appealed for peaceful demonstrations. Upon arriving at the Zócalo, a group of protesters burned a giant effigy of Peña Nieto, who has been criticized for his slow response to the disappearance of the students, and for traveling abroad in the midst of a national crisis. The evening of largely peaceful demonstrating ended with masked protesters clashing with authorities near the National Palace. Riot police forcefully cleared the plaza, corralling protesters with their shields and batons. Some 31 people were arrested out of an estimated 30,000 protesters, according to the police. Peña Nieto and other government officials have referred to the protests as a campaign to destabilize the government: "We have seen violent movements which hide behind the grief [over the 43 students] to stage protests, the aim of which at times is unclear," Peña Neito said earlier this month. They seem to obey interests seeking to generate instability, to foment social unrest. A crackdown to come? Violence on the part of protesters, as seen in recent weeks from groups trying to burn down the door to the national palace in Mexico City or blocking the Acapulco international airport and throwing fire bombs in Guerrero, allows "the government to position itself as a victim," Mr. Tirado says. It can allow for state, federal, and municipal forces to justify in the public opinion action against demonstrators. An editorial in the Mexican newspaper El Universal on Wednesday condemned violent protests as against the desires of the majority of Mexicans. The acts of vandalism that have taken place in protests over the disappearance of the 43 students from Ayotzinapa are unacceptable, because you can't ask for the end of violence through the use of violence. There is understandable anger and social indignation, but in no way does that make it ok to destroy buildings, private property, set fires, assault people and try to confuse an aggressive political agenda with that of a population that doesn't want fire, but wants peace.... There are more Mexicans that seek social justice through democratic means. The ideological differences in our political structure in this country are reflected in congress and in our democratic elections. This is our reality, and it must remain this way. Thursday's march took place on the 104th anniversary of the start of the Mexican Revolution, an uprising against dictator Porfirio Díaz. Erika Hernandez, a student at the University of the City in Mexico City dressed in all black for the march, says she is mourning the loss of the students, and her loss of "any confidence" in the government. "This is our modern day revolution," says Ms. Hernandez.