Under German rule the colonial administrators treated Nelson as an equal, but after New Zealand seized control in 1914, Nelson was excluded and alienated by the new government. Despite being elected to the Legislative Council in 1924, he could do little as he and the other elected members were constantly overruled by the more numerous government appointees. This treatment turned Nelson into one of the major forces in the Samoan independence movement, known as the Mau.
In May 1927 Nelson founded a newspaper, the Samoa Guardian, to support its claims. In response to his growing public dissent, the New Zealand administration tried to brand Nelson as unscrupulous and a trouble maker. The colonial administration's desperation to silence Nelson led them to exile him in January 1928, along with two other part-European members of the Mau. During his five years of exile, Nelson took his protests as far as the League of Nations in Geneva.