After the establishment of the ethnic Tai-Shan dynastic ruling factions in the area of Siam, the Burmese now had a rival on their eastern border. As a result a series of wars were fought over control of the cross country trading routes between the Arakan coast and the South China Sea. The wars were especially bitter when the dominant ethnic group in Burma was Burman or Mon rather than Shan. Local historians indicate that situation was often a stalemate unless the Burmese were united, thus attacking with an overwhelming force. By the 1500s, one side having superiority in military technology (cannon or muskets) could cancel the numbers advantage.

During most years, the campaigns were only conducted during the non-monsoon season. The monsoon floods would isolate the invader from their supply bases and increase losses due to disease caused by a lack of food. Retreats under such conditions often turned into routs. Some Burmese armies of reported as having lost over 50% of their initial invading force.

1412………Siam captures Martaban
1539………..Battle of Chiang Kraw. Siam with 120 Potuguese mercenaries defeat the Burmese
1548…………Siamese raid the Lower Burma area of Tavoy.
1548…………Burman-Talaing force including Portuguese (400 bodyguards + 180 mercenaries) with cannon and six ships invades Siam. The Burman try to capture Ayuthia and Kampengpet but fail with numerous losses. The Siamese raise a relief army in the north which assists in relieving the capital.

1548………..Battle of Supkanburi. Siam forces lead by the King, Queen and two Crown Princes are defeated. The Queen is killed during the battle.
1548……….Battle of Muang Kamphaengphet. Burmese army ambushes one several Siamese relief forces
1563-64…….Second Burman invasion of Siam. Aka White Elephant War. Using a much larger army, the Burman win several open battles against the Siamese. They capture Kamphaengphet, Sukhotai and even Ayuthia. The army is forced to return to Burma after reports of revolts in Lower Burma.

1563………Battle of Chainat. A lengthy battle characterized by two phases. The outnumbered Siamese army is able to halt the Burmese due to close fire support by Siamese war canoes. During the second phase, the Burmese are able to bring up their own supporting riverine fleet and drive the Siamese from the field.

1563………Battle of Lumphli Plain. Burmese forces capture key forts protecing approaches to Aythnia.
1563……..Battle of Hantra Plain. Burmese forces defeat a Champa reinforcement army which was advancing to assist the Siamese.
1568-69…….Third major Burman invasion of Siam
1581-1600….Lower Burma is subjected to continuous raids by Shan from Siam. In response, the Burmans launched five major invasions of Siam. All end in disaster.
1583……Siam + Talaings vs Burmese near Ava. Battle of Satong River. Siam won but still returned home.
1584…….Burmese invade Siam. The Bassein Corps (30,000) is defeated by the Siamese. The main Burmese force (100,000) advance from Chiang Mai and fight several battles with withdrawing Siamese (80,000) troops. A Chaing Mai force (5,000 horsemen) are defeated by an elite force of Siamese guard.

1584……Major Battle of Bang Kaeo which is fought outside Aythunia. A Siamese advance guard (10,000) engage the Burmese advance guard (15,000 cavalry). Both sides are reinforced by their main forces. Siam (30,000) vs Burmese (60,000). The Siamese win. 1586…Burmese (250,000) invade Siam and advance to siege the capital at Aythina. Several battle are fought. The Burmese assault fortified positions or fight Siamese sorties from the city. Burmese capture Phraya Nahon fort. The Siamese won at Bang Kradan. After a fierce battle it is a stalemate at Pa Mok.

1590….Burmese invade Siam. The Siamese defeat the Burmese at Ban Khoi

1592….Siamese forces (50,000 ? men) in five divisions invade the Burmese allies of Tavoy and Tenasserim. The Tavorians (30,000 ?) are defeated at the Battle of Banhat Hill. Tenasserim resists assaults for fifteen days before surrendering. The Siamese use them as a base to invade Lower Burma. Siamese troops being transported along the coast forces (3 European sloops + 150 war boats) engage the Burmese (10,000 men with 2,000 war boats). The Siamese are reinforced by 200 boats and win the battle (Ban Bao) 1592….Siamese + Talaing allies (80,000) defeat the Burmese (150,000) 1594…Siamese + Talaing are defeated by the Burmese near Satong.

1595…Siamese + Talaings vs Burmese. Siam Invades Upper Burma.
1599…Siam launches a Second invasion of Upper Burma. Siam allies with Chiang Mai. Assault on Toungoo is defeated thus ending the Siamese invasion