Spanish or Castilian is a Romance language in the Ibero-Romance group that originated in northern Spain, and gradually spread in the Kingdom of Castile and evolved into the principal language of government and trade. It was taken most notably to the Americas and also to Africa and Asia Pacific with the expansion of the Spanish Empire between the fifteenth and nineteenth centuries. Today, 329 million people speak Spanish as a native language, making it the world's second most spoken language in terms of native speakers. However, it is the fourth most spoken language in terms of total speakers. Mexico contains the largest population of Spanish speakers. It is also one of the six official languages of the United Nations.

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