During the 15th and 16th centuries, with its global empire that included possessions in Africa, Asia, South America, and Oceania, Portugal remained one of the world's major economic, political, and cultural powers. English, Dutch, and French interests in and around Portugal's well-established overseas possessions and trading outposts tested Portuguese commercial and colonizing hegemony in Asia, Africa, and the New World. In the 17th century, the lengthy Portuguese Restoration War (1640–1668) between Portugal and Spain ended the sixty-year period of the Iberian Union (1580–1640). According to a 2016 study, Portugal's colonial trade "had a substantial and increasingly positive impact on [Portugal's] economic growth". Despite its vast colonial possessions, Portugal's economy declined relative to other advanced European economies from the 17th century and onward, which the study attributes to the domestic conditions of the Portuguese economy.