The country went months without naming a new prime minister, only for Parliament to elect Srettha Thavisin, a candidate who many frustrated voters say represents the establishment.The election was supposed to be about change. Three months ago, Thai voters propelled the progressive Move Forward Party to a surprise victory. “A new day for the people has arrived,” said Pita Limjaroenrat, the party leader, as he paraded through the streets of Bangkok.On Tuesday, Thailand named a new prime minister, but it was not Mr. Pita. A coalition government was formed in Parliament, made up almost entirely of parties linked to the generals who led the last military coup. Move Forward is in the opposition.Now, many Thais are asking why the future they had voted for is looking so much like the past.“If you go around and talk to middle-class Thais at the moment, they’re saying, ‘What the hell did we have this election for, if this is the result that we get?’” said Christopher Baker, a historian of Thailand.Thailand, Mr. Baker said, is giving up a chance to “reverse the fact that it’s been going backward, in almost every sense, for the last 15 years.”Supporters of the Move Forward Party during a protest in Bangkok last month. No political party had ever been so explicit about changing the status quo in Thailand.Sakchai Lalit/Associated PressAs the second-largest economy in Southeast Asia and an ally of the United States, Thailand was once a powerful player in the region. More recently it has suffered from prolonged economic stagnation brought about by nine years of military rule under Prime Minister Prayuth Chan-ocha, the general who seized power in a coup in 2014. Mr. Prayuth has steered Thailand away from democracy and toward authoritarian rule — he cracked down on pro-democracy protests and oversaw the rewriting of a Constitution that gave the military more power.His term fueled rising public anger and frustration, culminating in mass protests in 2020. For the first time, disaffected young Thais questioned publicly the relevance of the country’s powerful monarchy, a topic previously considered taboo. They asked why Thailand needed a royal defamation law, one of the world’s strictest, that carries a maximum sentence of up to 15 years in prison.Move Forward capitalized on this anti-royalist, anti-military sentiment, which became the bedrock of the party’s progressive platform. It announced more than 300 policy proposals, including shrinking the military budget and breaking up big business. No political party had ever been so explicit about changing the status quo.“No one would have thought that the party whose policy is to reform the monarchy and the military could win” the election, said Aim Sinpeng, a senior lecturer in politics at the University of Sydney, in Australia. “I don’t think you can take that significance away, ever. It’s completely changed Thailand.”A portrait of Thailand’s king, in Bangkok. Young Thais have questioned publicly the relevance of the powerful monarchy, a topic previously considered taboo.Adam Dean for The New York TimesMove Forward’s election victory jolted the political elite, which quickly set the wheels in motion to block the party’s ascent. In the days after the election, the complaints against Mr. Pita piled up. The Constitutional Court suspended him from Parliament, pending a review of a case involving his shares in a now-defunct media company. The military-appointed Senate blocked him from becoming the prime minister during an initial vote. After that, the Constitutional Court said he could not be renominated for the position.When it became clear that the establishment was not going to allow Move Forward to form a government, Pheu Thai, the populist party founded by the former prime minister Thaksin Shinawatra, stepped in.Pheu Thai had been Move Forward’s partner in the initial coalition. It said it had to part ways with Move Forward and attempt to form its own coalition after it became clear that other conservative parties were not willing to work with Move Forward.Pheu Thai does not share Move Forward’s liberal agenda, though it has promoted itself as a pro-democracy party. Mr. Thaksin had battled the conservative establishment for decades. But as a billionaire businessman, he is essentially a member of the old guard. Since 2001, the political parties he founded have consistently won the most votes in every election — except for this year.For 15 years, Mr. Thaksin had lived in self-imposed exile to avoid a lengthy jail term on corruption and abuse of power charges, with one goal: to return home to Thailand.Democracy demonstrations in Bangkok in 2020.Adam Dean for The New York TimesOn Tuesday, he did that, just hours before Pheu Thai’s candidate, Srettha Thavisin, secured enough votes in Parliament to become the next prime minister.For many in Thailand, Mr. Thaksin’s timing only confirmed their suspicions that a quid pro quo arrangement had been made between Pheu Thai and the conservative establishment to have his prison sentence reduced in exchange for keeping the military and royalists in power.“Srettha was a product of this deal with the Thai establishment,” said Ruchapong Chamjirachaikul, a politics specialist at iLaw, a civil society organization. “The people don’t feel excited about having Srettha as prime minister.”To obtain enough support for Mr. Srettha, Pheu Thai relied on the military’s support, despite vowing repeatedly in the past to remove the generals from politics. Mr. Srettha, a real estate tycoon, says the party had no choice because of “basic math”: to secure the premiership, he needed 374 votes from both houses of Parliament, including the military-appointed Senate.“It’s not deceiving the people, but I have to say it bluntly that we have to accept reality,” Mr. Srettha, 61, said in a speech to Pheu Thai party members on Monday.Move Forward lawmakers voted against Mr. Srettha; they had announced earlier this month that they would do so because Pheu Thai was essentially extending military rule in Thailand. “There will never be a day that this crossbred government can make a difference in society,” Mr. Pita, 42, wrote on Facebook after Mr. Srettha was voted in on Tuesday.The question now is whether Mr. Srettha has the support to hold together an 11-party coalition government that is united in its determination to stop Move Forward but in agreement on little else. Analysts warn that such an unwieldy coalition could lead to more instability.Pheu Thai’s candidate, Srettha Thavisin, had to rely on the military’s support to secure enough votes to become prime minister.Lauren Decicca/Getty Images“It’s very much a government that’s held together by a common enemy, but that doesn’t make them automatically friends,” said Ken Mathis Lohatepanont, an independent political analyst who writes about Thai politics.Thailand’s neighbors and partners are watching developments with apprehension, fearing that political instability in one of the world’s most popular tourist destinations could derail economic cooperation.History warns that this is possible: For the past 70 years, Thai politics have been defined by a cycle of protests and coups — the country has had 13 successful coups in its modern history, and several more attempted ones. Except for Mr. Thaksin’s first term from 2001-2005 and Mr. Prayuth’s term, no government in Thailand has lasted its full term in the past two decades.Countries like the United States, which was quick to condemn Cambodia for a recent election that was deemed not to be free or fair, have been largely silent on the protracted election process in Thailand.Sunai Phasuk, a senior researcher on Thailand for Human Rights Watch, said the rights organization had been pressing the United States, the European Union and Australia to take a stronger stance but has been told these governments prefer a “wait and see” approach.Mr. Sunai added that the United States was probably being cautious about alienating Thailand to avoid driving it closer to China.Last month, the State Department said that it was “closely watching” developments in Thailand and that it was concerned about the recent legal cases against Mr. Pita, a graduate of Harvard and the Massachusetts Institute of Technology, and Move Forward.One complaint before the Constitutional Court centers on the party’s effort to amend the royal defamation law, calling it tantamount to “attempting to overthrow the democratic system with His Majesty the King as the Head of State.”A ruling against the party could lead to its dissolution.The Election Commission is also investigating Mr. Pita to see if he was aware that he could not run for office because he owned shares in a now-defunct media company. If found guilty, he could be imprisoned for up to 10 years.Muktita Suhartono More