Complex sentence: The territory represented one of the last remnants of the Spanish Empire, and was abandoned following international pressure, mainly UN decolonisation resolutions, as well as internal pressure from native populations and the external claims of Morocco and Mauritania.
Split into simpler sentences: The territory represented one of the last remnants of the Spanish Empire. It was abandoned following international pressure, mainly from United Nations resolutions regarding decolonisation, as well as internal pressure from native populations and the external claims of Morocco and Mauritania.