Amongst [the factors that contributed to the growing instability of the Vijayanagar kingdom] was the new Portuguese presence...According to one authority, 'the Portuguese have the dubious distinction of introducing politics into the [Indian] ocean.' Maritime trade had hitherto been considered as open to all and subject only to competitive pressures and local incentives. The Muslim traders and Islamic shipping interests had gained a near-monopoly of the sea-routes to the west and to the east had not therefore been cause for alarm. But as of the early sixteenth century the freedom of the seas and of the monsoon winds was called into question. Thanks to developments in navigation and naval gunnery, oceanic trade was suddenly revealed as susceptible to state direction and subject to military control. By demonstrating that maritime empire was a paying and practical proposition, the Portuguese had indeed politicised the Indian Ocean. Land-based empires which in any way depended on overseas trade would have to come to terms with it.
From India: A History, by John Keay.