Why did Tonga become a British protectorate in 1900?

Tonga became a British protectorate in 1900 primarily to discourage German advances in the region.1

During the reign of King George Tupou II, the kingdom entered into a treaty with Great Britain that established this protective status. Under the terms of this agreement—which was later amended in 1905—Tonga agreed to conduct all of its foreign affairs through a British consul. This consul was granted veto power over the kingdom's foreign policy and financial matters, though they were not to interfere in Tonga's internal affairs.12