Okay, so here's the skinny on what's going on in Thailand:
Like so many countries, there's a political dispute which has polarized into two camps (conveniently color-coded):
-- The Red Shirts: Primarily rural and poor, looking for increased social spending, government reforms, and a stronger government and weaker monarchy. Worth noting here that Thailand is a constitutional monarchy where lese majeste is still a thing; i.e. you can go to jail for criticizing or disrespecting the King. (For all that, the King himself has said he needs to be criticized if he's wrong and seems like an all-around okay guy.)
-- The Yellow Shirts: Primarily middle-class urbanites, capitalist, pro-royalist, deeply suspicious (and with some good reason) of the recent government because of a history of corruption and nepotism.
Backstory:
In the mid 2000-s, a billionaire reformer named Thaksin Shinawatra became PM of Thailand, and his supporters became the Reds. While his land and economic reforms were wildly popular with the rural poor, they pissed off a lot of business interests in Thailand, which eventually led to a military ouster in 2006 and Thaksin going into self-imposed exile to avoid arrest on corruption charges. There was considerable unrest at the time as the Red supporters saw this as an illegal coup. His political party was also dissolved.
Despite this, candidates allied with the Red Shirts continued to win general elections, usually to have their candidates shortly thereafter found guilty of some crime or another (often on questionable grounds) by the Thai Constitutional Court and tossed out of office. (One was found guilty of "conflict of interest" because he was the host of a popular TV cooking show.)
In 2008, the Democrat Party (the main Yellow Shirt party) was actually able to form a coalition government. By early 2009, the Red Shirts were out on the streets in force, arguing that the Yellows had essentially abused their control of the Constitutional Court (which is supposed to be non-partisan, like the US Supreme Court) to invalidate democratic elections until they could get a result they wanted. In 2010, these protests took an ugly turn when a firefight actually broke out between Thai Army units during an attempt to clear a protest. 87 were killed and 1300+ wounded.
In 2011, a Red Shirt-allied party won and the new PM was Yingluck Shinawatra -- the younger sister of deposed ex-PM Thaksin Shinawatra.
In late 2013, a former deputy PM from the 2008 Yellow Shirt government started publicly calling for an end to "the Thaksin regime" and encouraging street protests. At the same time, Yingluck's government attempted to pass a blanket amnesty for all people who had been charged with crimes relating to the 2010 unrest. This was amended at the last minutes to include *all* political crimes, including her brother's 2006 corruption charges. Many thought this was just clearing the way for him to return to the country and run for election again (which many Yellow Shirts saw/see as hopelessly rigged), and the protests ballooned.
The Yellow Shirts began demanding that the government be dissolved, and replaced with an unelected "People's Council", stating that elections could not be trusted because the Shinawatra family's influence was so pervasive in the Thai political system (except, it would seem, for the Constitutional Court). In response, Yingluck dissolved Parliament in February and stated there would be new elections.
On May 7th, the Constitutional Court ruled that Yingluck had abused her power by replacing a high-level official with Thaksin Shinawatra's brother-in-law and would have to step down as President. The Red Shirts saw this as yet another "judicial coup" and took to the streets even as the Yellow Shirts were on the streets demanding that the entire damn government be dissolved and replaced with this unelected body.
Unrest escalated into violence over a couple of weeks until finally last night, the Thai Army decided to institute martial law (without informing the government, apparently) to put a halt to things.
So....yeah. Thailand is a bit of a basket case politically. Both sides have some legitimacy to their complaints, and yet both sides obviously have some egregious abuses of power to answer for.