The king provided fleets and elephants to rush through Burmese forests and sent Siamese armies to participate in the invasion of Burma when the British promised to offer Siam the conquered lands.
2.In B.E. 2369, the king negotiated the first trade-treaty of Siam with the British -the Treaty of Amity and Commerce (Siam–UK) or the Burney Treaty (Henry Burney-the British negotiator). Under the treaty: Siam must…
give mining concessions to Britain in exchange with Thai independence
establish a uniform taxation system
reduce taxes on foreign trade
abolish some of the royal monopolies (controls)
The British wanted more trading concessions and pressured King Rama III to grant these.
(The king managed to resist and refuse to extend the provisions of the Burney Treaty.)