A new and possibly dangerous chapter in Thailand’s volatile political history begins on Sunday, when the country goes to the polls in an election widely expected to bring Yingluck Shinawatra, sister of exiled former leader Thaksin Shinawatra, to power.

For more than a decade following a bloody standoff with the army in 1992, Thailand had seemed to be settling down to stability and democracy, albeit one that still reserved considerable power for the monarchy and the military establishment. But in 2006 Thaksin, having been re-elected in a landslide the previous year, was confronted by popular demonstrations by the People’s Alliance for Democracy, or “yellow shirts”, and eventually overthrown in a military coup.

Charged with corruption, abuse of power and human rights violations, Thaksin has lived overseas for most of the past five years. But when elections were held again, in December 2007, his influence was still strong enough to secure the victory of his political allies, then called the People Power Party.

Further protests followed, and in 2008 the establishment was able to coerce enough MPs to switch sides to put the Democrat Party, ally of the yellow shirts, into power, under current prime minister Abhisit Vejjajiva. Thaksin’s supporters — the “red shirts” — took to the streets in their turn, until they were crushed by a government crackdown in May 2010.

Now Thaksin’s forces, this time rebranded as the Pheu Thai Party, again look like turning their strong support among the rural poor into a parliamentary majority. Abhisit’s chances are further harmed by the fact that his former allies, the yellow shirts, are campaigning for a “none of the above” vote, on the basis that the current crop of politicians are all equally corrupt and useless.

By the standards of the region, Thailand is still a relatively free and open country. The economy is healthy, and the election campaign has been largely peaceful. It does not have the feel of a country on the edge of civil war.

But if Yingluck’s lead in the polls is borne out on Sunday, no one knows what happens next. Writing in the pro-Thaksin Bangkok Post today, Suranand Vejjajiva asks “After five years of intense conflict and escalating violence, will the establishment just simply give in to Thaksin — or vice versa, with Thaksin lying low and letting a compromise be worked out? No chance, so far.”

The establishment, of course, has its own conflicts to deal with, preoccupied by the impending but unmentionable battle over the royal succession to the ailing 83-year-old king Bhumibol. (The queen is a patron of the yellow shirts, while the crown prince is said to be closer to Thaksin.)

That means the stakes are unusually high, but it also means the army may be more than usually reluctant to intervene, at least until it works out just which way the winds are blowing. Army chief Prayuth Chan-Orcha reportedly said yesterday that “There is no thought of having a coup … Whichever party forms a government, the military will do their duty and follow [its] orders”.

Thaksin and his sister will  be hoping that this time the generals really do mean to let democracy take its course.