Smuggling was carried on to a considerable extent for years, and in 1891 a fresh stimulus was given to contraband by the introduction of a Protectionist Tariff, which came into force on April 1 of that year, and under which Spanish goods brought in Spanish ships were allowed to enter free of duty. [126] In order to evade the payment of the Manila Port Works Tax (q.v.), for which no value was given, large quantities of piece-goods for Manila were shipped from Europe to Yloilo, passed through the Custom-house there and re-shipped in inter-island steamers to Manila. In 1890 some two-thirds of the Yloilo foreign imports were for re-shipment. The circumstances which directly led to the opening of Zamboanga (in 1831) as a commercial port are interesting when it is remembered that Mindanao Island is still quasi-independent in the interior--inhabited by races unconquered by the Spaniards, and where agriculture by civilized settlers is as yet nascent. It appears that the Port of Jolo (Sulu Is.) had been, for a long time, frequented by foreign ships, whose owners or officers (chiefly British) unscrupulously supplied the Sulus with sundry manufactured goods, including _arms of warfare_, much to the detriment of Spanish interests there, in exchange for mother-of-pearl, pearls, gums, etc. The Spaniards claimed suzerain rights over the island, but were not strong enough to establish and protect a Custom-house, so they imposed the regulation that ships loading in Jolo should put in at Zamboanga for clearance to foreign ports. The foreigners who carried on this illicit traffic protested against a sailing-ship being required to go out of her homeward course about one hundred and twenty miles for the mere formality of customs clearance. A British ship (and perhaps many before her) sailed straight away from Jolo, in defiance of the Spaniards, and the matter was then brought to the notice of the British Government, who intimated that either Jolo must be declared a free port or a Custom-house must be established there. The former alternative was chosen by the Spaniards, but Zamboanga remained an open port for foreign trade which very rarely came. The supreme control of merchant shipping and naval forces was vested in the same high official. No foreigner was permitted to own a vessel trading between Spain and her colonies, or between one Spanish colony and another, or doing a coasting trade within the Colony. This difficulty was however readily overcome, and reduced to a mere ineffective formality, by foreigners employing Spaniards to become nominal owners of their vessels. Thus a very large portion of the inter-island steamer carrying-trade was virtually conducted by foreigners, chiefly British.