Already a global power, the Spanish defeated powerful adversaries such as the Aztecs and Incas in the Americas by exploiting existing conflicts and rivalries between tribes and nations between the 15th and 18th centuries.
(Note: and also by accidentally spreading disease; it wasn't all strategy. -JM)
Acquisitive and protective of the supply of precious metals its new colonies afforded it, the Spanish Empire enthusiastically participated in the Atlantic slave trade and defended its trade routes aggressively.
In 1701 Spain became embroiled in the War of Spanish succession. At once international and civil, it ended with a series of treaties, in 1713 and 14, that saw King Philip the V remain in power, but lose his line to the French throne.
(Note: Let's face it. He wasn't really using that thing anyway. -RL)
Moreover, Philip kept his title of "Overseas Emperor" but relinquished much of his empire to the British, who were granted the exclusive right to slave trading in Spanish America for thirty years.
The century was nevertheless one of prosperity for the Spanish Empire, as their trade reputation grew steadily under Bourbon oversight and continued to grow at an extraordinary rate until the 1780's.
(Note: Gosh, I'm so glad they recovered from that slave-trading loss. Philip V, what a trouper. -JM)