After a period of bloody dynastic struggle at the beginning of the 18th century, Ayutthaya entered into what has been called the golden age, a relatively peaceful episode in the second quarter of the eighteenth century when art, literature, and learning flourished, but it was simply the calm before the storm.

There were foreign wars even then, and Ayutthaya fought with the Vietnamese for control of Cambodia starting around 1715. But a greater threat came from Burma, where the new Alaungpaya dynasty had subdued the Shan states.

The last fifty years of the kingdom witnessed a bloody struggle among the Thai princes. The throne was their prime target, and purges of court officials and able generals followed. The last monarch, Ekathat, originally known as Prince Anurakmontree, forced the king, who was his younger brother, to step down and took the throne himself.

The Burmese invaded more than once. The first war being fought in 1759–1760 when 40,000 Burmese troops led by Alaungpaya and his son Hsinbyushin invaded down the Tenasserim coast from Martaban. Their battle plan was to go around the heavily defended Siamese positions along shorter, more direct invasion routes. The invasion force overran relatively thin Siamese defenses in the coast, crossed the Tenasserim Hills to the shore of the Gulf of Siam, and turned north towards Ayutthaya.

Taken by surprise, the Siamese scrambled to meet the Burmese in the south, and put up spirited defensive stands en route to Ayutthaya. But battle-hardened Burmese forces overcame numerically superior Siamese defenses and reached the outskirts of Siamese capital on 11 April 1760. But only five days into the siege, the Burmese king suddenly fell ill and the Burmese command decided to withdraw.

In 1765, a combined 40,000-strong force of Burmese armies led by King Hsinbyushin invaded the territories of Ayutthaya from the north and west. Major outlying towns quickly capitulated, and after a 14 months' siege, the city of Ayutthaya capitulated and was sacked in April 1767. Ayutthaya's art treasures, the libraries containing its literature, and the archives housing its historic records were almost totally destroyed, and the Burmese brought the city of Ayutthaya to almost complete ruin.

The utter destruction that was wrought on this once flourishing city is evident even today, when one walks round the ruins and tries to imagine what they must have looked like in their heyday. A great many treasures would surely have passed down to mankind if only this destruction had been avoided, but which are now lost forever.

When it was at its height in the mid 17th century Ayutthaya was probably the largest city in the world, having around 1,000,000 inhabitants (as a comparison, London at that time, in Shakespear's period, had around 50,000), and had embassies and envoys from all over the known world, and even whole villages had been set up to accommodate them.

For all that the Burmese rule lasted a mere few months. The Burmese, who had also been fighting a simultaneous war with the Chinese since 1765, were forced to withdraw in early 1768 when the Chinese forces threatened their own capital. With most Burmese forces having withdrawn, the country was reduced to chaos.

One general, Phraya Taksin, former governor of Taak, began the reunification effort. He gathered forces and began striking back at the Burmese. He finally established a capital at Thonburi, across the Chao Phraya from the present capital, Bangkok, and Taksin ascended the throne.

The ruins of the historic city of Ayutthaya and associated historic towns in the Ayutthaya historical park have been listed by UNESCO as a World Heritage Site. The modern city of Ayutthaya was refounded near the old city, and is now capital of the Ayutthaya province.