In 1900, amid the backdrop of increasing European imperialism in the Pacific, Great Britain formally annexed the Kingdom of Tonga. The decision to annex Tonga was significantly influenced by King George Tupou II, who, recognizing the potential threats from neighboring colonial powers and the desire to ensure Tonga's sovereignty, sought British protection. The annexation was part of Britain’s broader strategy to secure its interests in the region and to provide a buffer against the expansion of other powers, notably Germany and the United States, who were also vying for influence in the Pacific islands.

The formal annexation followed a series of treaties that had established British control over Tonga's foreign affairs, beginning with a Treaty of Friendship in 1876. The standing arrangement included provisions that allowed British consuls to influence Tongan political decisions, signaling a shift in Tongan governance. The official announcement of annexation not only highlighted Tonga's unique position as one of the few Pacific monarchies but also reflected the complexities of colonial dynamics in the area, where indigenous leaders had to navigate their autonomy in the midst of colonial rule.

With this annexation, Tonga retained its monarchy and internal governance, which was a significant distinction from other Pacific islands that were fully colonized and lost their leadership structures. However, the agreement brought Tonga under British protection, and issues around local governance became intertwined with the interests of the British Empire, leading to a complex relationship that defined Tonga's political landscape well into the 20th century.