The USA: the beginning of imperialism

In the 1890s  the Frontier was ceasing to exist. Up to that time the Frontier had been a an essential part of of the American dream of freedom and opportunity.
Thus began the imperialistic policy of the USA, almost as a compensation for the loss of the internal frontier.
In 1898 the USA annexed the Hawaian Island and in the same year waged a short war against Spain in Cuba, to defend the economic interests on the island. However Cuba became a free republic a few years later.
In 1903 the President Theodore Roosvelt obtained the lease of the Panama Canal Zone Thus enlarging the American territory with strategic positions.