Bangkok, March 25 -- Thailand's election Sunday is likely to produce a weak, unstable government whether it's a civilian or military-backed party that cobbles together a coalition, setting off a new phase of uncertainty in a country that's a U.S. ally in Southeast Asia and one of the world's top tourist destinations.

The election is Thailand's first since its military seized power from an elected government in May 2014. It was the conservative establishment's third major attempt by either military or legal coup to eradicate the influence of former Prime Minister Thaksin Shinawatra, a tycoon who made his fortune in telecommunication and upended Thailand's politics with a populist political revolution nearly two decades ago.

Prime Ministe...