The Berlin Conference of 1884 regulated European colonisation and trade in Africa. New Imperialism rose on the back of newly industrialised nations Germany and Japan. 'New' imperialism because the first wave between C15th and early C19th focused on the Americas, after 'losing' the Old World conflict to Muslim powers which barred the path east and into North Africa. The "Civilising Mission" religious justification combined with trade wars between European powers. Instead of just ports, the conference required "effective occupation". Germany, being a new power, insisted that no European state could have a hand-wavy 'claim' without strong and effective political control.
This concept extended beyond Africa in the new attempt to "fill the gaps". Instead of the commercial venture before, it became a 'moon-landing' style pissing contest. In 1893, Britain defined its area of interest in the Solomon islands. It was declared a British Protectorate. A protectorate was a de-facto colony, but used a chosen pre-existing native state as an agent of indirect rule. Sometimes the Protected State, didn't actually agree to the protection, and sometimes the additional foreign muscle bolstered dubious local claims. The Solomon Islands gained independence in the post-World War II wave of self-determination. This was added to the increased cost of administering colonies becoming evident after the 1973 oil shocks. Again, a commercial decision, with a convenient justification. Independence came in 1978, with Queen Elizabeth II remaining the Constitutional Monarch.