'this's his tactics How to kill 2 bird with 1 stone :
In Kertanegara's era ( The last King of Singhasari kingdom ), a messenger from Mongol Emperor, Kubilai Khan came to Singhasari and ordered Singhasari recognized the power of Mongol. Kertanegara took the order as insult and punished the messenger in his face. Before the mongol had their revenge, Jayakatwang, king of Kediri, one of fief of Singhasari, rebelled and killed Kertanegara,but Kertanegara son in law Raden Vijaya save and run to Madura island with revenge on his heart.
When the Mongol soldiers came in Imperial Yuan fleet, Kertanegara's son in law, Raden Vijaya, made an Allied with them, sending small of His army to helping them and manipulate them into fighting with Jayakatwang. The Mongol didn't realize that they destroyed different kingdom. Before they realized what had happened, Raden Vijaya with His largest Army attacked his former allies,Happiness but tired Mongol soldiers didnt expecting that while on the other side the remnant of Raden Vijaya soldiers whom are helping the Mongols Ruined Jayakatwang's kingdom Backstabing The mongols from Behind kickassed the mongols until they fled from Java.
Raden Vijaya founded his own kingdom,The greatest Kingdom in South East asia History The kingdom of Majapahit.