Causes
Further information: Burmese invasions of AssamBy 1822, Burmese conquests of Manipur and Assam had created a long border between British India and the kingdom of Ava. The British, based in Calcutta, had their own designs on the region, and actively supported rebellions in Manipur, Assam and Arakan. Calcutta unilaterally declared Cachar and Jaintia British protectorates, and sent in troops. Cross border raids into these newly acquired territories from British territories and spheres of influence vexed the Burmese. Convinced that war was inevitable, Burmese commander in chief Bandula became a main proponent of offensive policy against the British. Bandula was part of the war party at Bagyidaw's court, which also included Queen Me Nu and her brother, the lord of Salin. Bandula believed that a decisive victory could allow Ava to consolidate its gains in its new western empire in Arakan, Manipur, Assam, Cachar and Jaintia, as well as take over eastern Bengal.
In January 1824, Burmese sent in one of his top lieutenants Thado Thiri Maha Uzana into Cachar and Jaintia to chase away the rebels. The British sent in their own force to meet the Burmese in Cachar, resulting in the first clashes between the two. The war formally broke out on 5 March 1824, following border clashes in Arakan.
The British reason for the war was in addition to expanding British Bengal's sphere of influence, the desire for new markets for British manufacturing. The British were also anxious to deny the French the use of Burmese harbours and concerned about French influence at the Court of Ava, as the kingdom was still known to them. Symes's mission was fully equipped to gain as much knowledge as possible of the country for future British plans whereas previous envoys were concerned principally with trade concessions. Anglo–French rivalry had already played a role during Alaungpaya's endeavours of unifying the kingdom. The Burmese in these wars were advancing into smaller states not ruled by the British or the subject of expansionary goals by the British before the war began, and the British were not so much preoccupied by the refugee problem initially as by the threat posed by the French until further incidents forced their hand.
Read more about this topic: First Anglo-Burmese War