I always love a digression. When guys veer off a topic, sometimes ya get the most fantastic things.
Yess, the jungle was the natural fortress of many SEAn kingdoms.
Anyway. Of all their opponents, the Javanese were the most interesting in the way they dealt with the offspring of All-Go-Die Khan.
Emperor Kublai had sent envoy Meng Qi to the court of Kerta Negara, king of Singha Sari kingdom with a typical proposal, i.e. for the Javanese king to submit and pay tribute.
Kerta Negara branded Meng Qi's face with a hot iron, the normal punishment for a common thief, cut off his ears, then sent him packing back to Beijing, by then the Mongol empire's capital.
Kublai responded with 20,000 fighters on 1,000 ships. By the time they arrived, Jaya Katwang, king of vassal kingdom Kediri, had risen against Kerta Negara, killed him and usurped his kingdom.
Raden Wijaya, son-in-law of Kerta Negara, received the invading Mongols as allies, pledged his vassalage, and told them (lied to them) that the culprit to be punished was Jaya Katwang (the new king of Singha Sari), who, unbeknownst to the new batch of Mongols, actually had nothing to do with Meng Qi's fate.
The combined armies of Raden Wijaya and the Mongols routed Jaya Katwang's army. Raden Wijaya then requested permission to return to his newly founded home kingdom, Majapahit, to prepare tribute, while leaving the Mongols in Singha Sari to celebrate their victory. When 200 unarmed Mongols went to Raden Wijaya's court to collect the promised tribute, they were ambushed and destroyed by Raden Wijaya's soldiers.
Raden Wijaya's main army pressed onward back to Singha Sari, pretended to join in the victory celebrations with their Mongol 'allies' for a while, then turned on them and attacked them with all their strength.
The bewildered, boozed-out Mongols had to beat a hasty retreat and put out to sea fast, because the North Easterly monsoon winds to carry them home was due to end soon, which would leave them vulnerable in unfamiliar, hostile terrain for the next 6 months. They lost 3,000 of their best fighting men, and never came back again. While Majapahit later rose to become the new most powerful kingdom of Java.