Sugar plantations were the backbone of the europeanamericanhawaiian economy. sugar was also the main hawaiian export to the united states. for many years, hawaiian sugar was sold tariff-free in the united states. in 1890, the us congress passed the mckinley tariff acttariff treaty of nanjingtariff treaty of kanagawa, which removed tariffs on all foreign sugar imports. this change meant that hawaiian sugar producers had to compete with other nations in the us market.