Port cities have long played a critical role in the circulation of peoples, commodities, and ideas within and across the maritime spaces of Southeast Asia. Although an indelible component of the islands and archipelagos of this region since at least the 15th century, the rise of global empires in the 19th century rejuvenated these communities by the sea, giving rise to thriving metropolises from Rangoon to Singapore, Bangkok to Penang. Historians recognize that these ascendant cities served as “imperial bridgeheads,” connecting the products and peoples of the Southeast Asian hinterlands to world markets. Yet, the idea of “cosmopolitanism” arguably pervades how historians understand these port cities; bustling docks, diverse populations, and lively scenes of popular culture take precedence over the imperial coercion unfolding within and beyond their shores. Port cities and urbanization, in fact, were intimately intertwined with the violence of conquest and Islamic insurgency enveloping various corners of the Southeast Asian countryside. When armed conflicts such as the bitter Dutch-Aceh War in the Netherlands East Indies (present-day Indonesia) and the Moro Wars in the southern Philippines engulfed venerable Muslim sultanates, the maritime metropolises of the Straits Settlements emerged as critical nodes—sites for the dissemination of weapons and smugglers, spies and diplomats, contentious ideas and theologies. These circulations were facilitated not just by Muslim networks or colonial agents but by the very cosmopolitan nature of port cities. Chinese and German, Arab and Turkish, Muslim and Christian, all became drawn into the whirling vortex of “Islamic insurgencies.” By highlighting the integral position of port cities in the conduct of various armed conflicts, it becomes possible to gain new perspectives and suggest reconfigured research paradigms for understanding the connected histories of colonial conquest.