Spain
When other Europeans explored, like Hernán Cortés and Francisco Pizarro, they found out that there were two continents there - North America and South America.  Spanish conquistadores took over very large parts of those two continents. This empire did not make Spain a rich country, for most of the money had to be spent in wars in Italy and elsewhere.  Some of these wars were fought against other European countries who were trying to take over parts of the Americas.