The Mataram conquest of Surabaya or Mataram-Surabaya War was a military campaign by the Sultanate of Mataram in the early 17th century that resulted in the capture of the Duchy of Surabaya (Kadipaten Surabaya) and its allies in eastern Java, in modern-day Indonesia. Prior to this conquest, Mataram and Surabaya were rivals for power in central and eastern Java. The campaign began in 1614 when Mataram, under the leadership of Sultan Agung, attacked Surabaya's allies, including Wirasaba. Surabaya and its allies launched a counterattack but were defeated near Pajang in 1616. Over the next few years, Mataram gradually conquered members of the Surabayan alliance, and by 1620, the city of Surabaya itself was under siege, holding out until it surrendered in 1625. With this conquest, Mataram unified most of central and eastern Java under its control, and cemented its position as the dominant power in Java. Surabaya and other conquered areas would remain in Mataram's hands until it was ceded to the Dutch East India Company in 1743.
Background
In the latter half of the 16th century, the Sultanate of Demak, the dominant power on the island of Java, disintegrated into several independent states. At the turn of the 17th century, three of these states emerged as the leading powers: the Sultanate of Banten in western Java, the Sultanate of Mataram in inland central Java, and the Duchy of Surabaya in coastal eastern Java. Mataram consolidated its power by absorbing other principalities: Pajang in , Demak (1588), Madiun (), and Kediri (1591). Following Mataram's unsuccessful westward expedition against Banten in about 1597, Mataram turned its expansion eastward, into areas under the influence of Surabaya.
The Duchy of Surabaya was centered roughly in today's city of Surabaya on the northern coast of eastern Java. It was a wealthy and powerful state, and the city was an important port in the trade route between Malacca and the Spice Islands. The city was approximately in circumference, and was fortified by canals and cannons. Allied with the nearby state of Pasuruan, the Duchy expanded its influence throughout the eastern part of Java in the beginning of the 17th century. By 1622, it was in control of Gresik and Sedayu in eastern Java. It was also the overlord of Sukadana and Banjarmasin in southern Borneo. More doubtful reports said it might have also extended its influence to Pasuruan, Blambangan, the Brantas valley region, and Wirasaba. Other than these, Surabaya was also allied with Tuban, Malang, Kediri, Lasem, all in eastern Java, as well as Madura off the northern coast. This alliance was primarily a response to the growing power of Mataram, and Surabaya was the founder and the most powerful member.
Campaign
Conquest of Surabaya's allies
In 1613 Hanyakrakusuma (r. 16131645, later titled Sultan Agung, "the Great Sultan", and referred to in literature with that title) rose to the throne of Mataram. He began the eastward conquest by an incursion towards Surabaya's southern flank, the Eastern Salient, Malang, and possibly Pasuruan in 1614. Surabayan forces attacked this Mataram army during its homeward march, but was defeated. In 1615 Agung conquered Wirasaba, personally leading the troops there. Surabaya did not commit its troops to help Wirasaba, due to the fear that its other ally, Tuban, would take advantage, betray Surabaya, and attack it from the rear.
The conquest of the strategically important Wirasaba posed such a clear threat to Surabaya and other eastern states that the alliance rallied. They mobilized their troops and marched towards Pajang, a city under Mataram's control but ostensibly on the verge of rebellion. However, a Mataram spy in Tuban deceived the allied forces into taking a bad route towards Pajang. As a result, the allied army found itself isolated in Siwalan, near Pajang. This army was surrounded by Sultan Agung and defeated in January 1616.
Agung then won victories in Lasem (1616) and Pasuruan (1616–17). In 1617 Pajang finally rebelled against Mataram but was defeated, and the lord of Pajang fled to Surabaya. In 1619 Agung conquered Tuban, one of the strongest members of Surabaya's alliance. This conquest put Agung in control of Tuban's shipbuilding activities, and therefore allowed him to build a navy to challenge Surabaya's previous naval supremacy.