a colonial empire is a collective of territories (often called colonies), either contiguous with the imperial center or located overseas, settled by the population of a certain state and governed by that state.
before the expansion of early modern european powers, other empires had conquered and colonized territory, such as the romans in iberia, or the chinese in what is now south china. modern colonial empires first emerged with a race of exploration between the then most advanced european maritime powers, portugal and spain, during the 15th century. the initial impulse behind these dispersed maritime empires and those that followed was trade, driven by the new ideas and the capitalism that grew out of the european renaissance. agreements were also made to divide the world up between them in 1479, 1493, and 1494. european imperialism was born out of competition between european christians and ottoman muslims, the latter of which rose up quickly in the 14th century and forced the spanish and portuguese to seek new trade routes to india, and to a lesser extent, china.
although colonies existed in classical antiquity, especially amongst the phoenicians and the ancient greeks who settled many islands and coasts of the mediterranean sea, these colonies were politically independent from the city-states they originated from, and thus did not constitute a colonial empire.