Given the task definition and input, reply with output. You need to read the given passage and construct a question about the information present in the passage. The question should be answerable from the passage. Most importantly, only those questions are allowed whose answers cannot be determined from a single sentence. Do not generate questions that require only a single sentence to answer. Instead, try to combine two sentences and create a question from that combination. Do not create open-ended questions, i.e., the answers to them cannot be found precisely from the information provided in the passage.

Paragraph- Sent 1: To protect its seagoing interests and trade routes, Portugal established strategic garrisons in Goa (India), Malacca (East Indies), and Hormuz in the Persian Gulf.
Sent 2: Portuguese explorers then embarked upon Macau (now Macao), the Congo, and various other parts of Africa, including the Sudan.
Sent 3: The Portuguese policy was to avoid armed strife and to develop a trade empire, rather than to conquer nations.
Sent 4: To this end it succeeded with relatively few blood-soaked episodes in its colonial history.
Sent 5: Adventures abroad, however, proved disastrous during the second half of the 16th century.
Sent 6: In 1557 the 14-year-old boy-king Sebastião ascended the throne, the beginning of a calamitous reign that was to end at the battle of Alcacer-Quiber (Morocco) in pursuit of a vain crusade.
Sent 7: Sebastião's untimely demise, alongside some 18,000 ill-prepared, badly led followers, set the stage for a crisis of succession.
Sent 8: For many years afterwards, legends and rumors bizarrely insisted that the king was still alive, and imposters turned up from time to time claiming the throne; those who were plausible enough to be deemed a threat were summarily executed.
Sent 9: In fact, the only rightful claimant to the crown was the elderly Prince Henry.
Sent 10: But after two years of alternating between the throne and his sickbed, he died, heirless.
Sent 11: Surveying the situation and smelling an opportunity, Spain occupied the power vacuum, and Portugal's neighbor and long-time antagonist became its master.
Sent 12: Spanish rule dictated Portugal's inadvertent involvement in Spain's ongoing wars.
Sent 13: In 1587 a squadron of British ships commanded by Francis Drake attacked the Algarve (now a "legitimate target" as Spanish territory) and sacked Sagres, thus depriving the world of the relics of Henry the Navigator.
Sent 14: Nine years later Faro was torched.
Sent 15: The 1386 Treaty of Windsor, by which Britain and Portugal had pledged eternal friendship, seemed a distant memory.
Sent 16: Portugal's empire was gradually eroded, and many of its trading posts (with the notable exception of Brazil) were picked off by the British and Dutch.
Sent 17: Finally, after 60 years of Spanish rule, Portuguese noblemen (aided by the French, then at war with Spain) organized a palace coup and restored independence.
Sent 18: The Great Disaster Portugal's greatest misfortune struck on All Saint's Day, 1 November 1755.

What created a power vacuum that was taken advantage of by Spain?