In the eighteenth century, a series of socio-economic and political changes within the kingdom, coupled with internal succession conflicts, left Ayutthaya militarily weakened and thus unable to effectively deal with a renewed series of Burmese invasions, in 1759–60 and 1765–67, from the new and expansionistic Konbaung dynasty of Burma, determined to eliminate their long-time rivals in Ayutthaya. In April 1767, after a 14-month siege, the city of Ayutthaya fell to besieging Burmese forces and was pillaged and completely destroyed, ending the 417-year-old Ayutthaya Kingdom. The seat of Siamese authority was then moved to Thonburi, and later Bangkok, in the following years.