Sugar plantations were the backbone of the european american hawaiian 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 act tariff treaty of nanjing tariff 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.