It was an agreement between the United States and the Kingdom of Hawaii that allowed for duty-free importation of sugar and other agricultural products from Hawaii to the United States. The immediate effect of the treaty was positive for Hawaii as it led to a significant increase in sugar exports to the US, which in turn brought more money and prosperity to the island nation.
However, the long-term effect of the treaty was negative for Hawaii because it resulted in the overproduction of sugar, which led to a dependence on the American market and a lack of diversification in the Hawaiian economy. Additionally, the treaty led to an influx of American and European settlers to Hawaii, which ultimately led to the overthrow of the Hawaiian monarchy and the annexation of Hawaii by the United States in 1898.
The treaty also had a negative impact on native Hawaiians, they were displaced and dispossessed from their land, and their society got impacted with the influx of foreigners who controlled most of the economy.