Oaxaca is occasionally riven by strife - demonstrating angry locals and heavy-handed "aguacates" (avocadoes, the name for the green-clad soldiers, who often arrived crammed in army trucks like - crates of avocadoes) getting into big hassles with injuires on both sides, in rural areas and in the city.
Here's the current deal: 10,000 teachers in Oaxaca have been striking for some time (this year,) and have taken over the Zocalo (central square.) The authorities have occasionally cracked down on them badly. The governor is moving his offices around from place to place, and there have been protests and counter-protests by supporters and a few opponents. I think
this article is the most accurate I have read - given my many years' living in Mexico, my familiarity with politics in various states including my beloved Oaxaca, and my onoging contacts with people connected with internal national issues.
Businesses have been picketed and vandalized, streets have been blockaded, a number of teachers and their supporters have taken to sleeping in the Zócalo and the streets (those blue tarps,) and many services have been disrupted. Many tourists have wisely left town, hotels have been vandalized.
Recently things have been made worse by the big brouhaha over the presidential election - both candidates have declared themselves winners, and many in Oaxaca (which supported Mr. Andrés Manuel López Obrador "AMLO" pretty heavily,) have joined in the demonstrations.
It's a good time to stay away right now, frankly; the stridency and actions have escalated the last few weeks.