Throughout the 17th century, the increasing predations and surrounding of Portuguese trading posts in the East by the Dutch, English and French, and their rapidly growing intrusion into the Atlantic slave trade, undermined Portugal's near monopoly on the lucrative oceanic spice and slave trades.
This sent the Portuguese spice trade into a long decline.
 The diversion of wealth from Portugal by the Habsburg monarchy to support the Catholic side of the Thirty Years' War also created strains within the union, although Portugal did also benefit from Spanish military power in helping to retain Brazil and in disrupting Dutch trade.
These events, and those that occurred at the end of Aviz dynasty and the Iberian Union, led Portugal to a state of dependency on its colonies, first India and then Brazil.

The joining of the two crowns deprived Portugal of a separate foreign policy, and Spain's enemies became Portugal's.
England had been an ally of Portugal since the Treaty of Windsor in 1386.
War between Spain and England led to a deterioration of the relations with Portugal's oldest ally, and the loss of Hormuz.
English help provided by Elizabeth I of England in a rebellion against the kings assured the survival of the alliance.
War with the Dutch led to invasions of many countries in Asia, including Ceylon (today's Sri Lanka), and commercial interests in Japan, Africa (Mina), and South America.
Even though Portuguese were unable to capture the entire island of Ceylon, they were able to keep the coastal regions of Ceylon under their control for a considerable time.
Brazil was partially conquered by both France and the Seventeen Provinces.

In the 17th Century, taking advantage of this period of Portuguese weakness, many Portuguese territories in Brazil were occupied by the Dutch who gained access to the sugarcane plantations.
John Maurice, Prince of Nassau-Siegen was appointed as the governor of the Dutch possessions in Brazil in 1637 by the Dutch West India Company.
He landed at Recife, the port of Pernambuco, in January 1637.
By a series of successful expeditions, he gradually extended the Dutch possessions from Sergipe on the south to São Luís de Maranhão in the north.
He likewise conquered the Portuguese possessions of Elmina Castle, Saint Thomas, and Luanda, Angola, on the west coast of Africa.
After the dissolution of the Union in 1640, Portugal reestablished its authority over the lost territories of the Portuguese Empire.
The Dutch intrusion into Brazil was long lasting and troublesome to Portugal.
The Seventeen Provinces captured a large portion of the Brazilian coast including Bahia (and its capital Salvador) and Pernambuco (and its capital Olinda).
The whole Brazilian northeast was occupied but the Dutch conquest was short lived.
The recapture of Salvador by a Spanish-Portuguese fleet in 1625 was followed by a rapid recovery of the lost territories.
The Dutch returned in 1630 and captured Recife and Olinda in the captaincy of Pernambuco, the largest and richest sugar-producing area in the world.
This began a war over Brazil, which would see the Dutch establish a colony called New Holland.
However, the Second Battle of Guararapes, second and decisive battle in a conflict called Pernambucana Insurrection, ended the Dutch occupation of the Portuguese colony of Brazil.

On the other hand, the Iberian Union opened to both countries a worldwide span of control, as Portugal dominated the African and Asian coasts that surrounded the Indian Ocean, and Spain the Pacific Ocean and both sides of Central and South America, while both shared the Atlantic Ocean space.
Throughout the 17th century, the increasing predations and surrounding of Portuguese trading posts in the East by the Dutch, English and French, and their rapidly growing intrusion into the Atlantic slave trade, undermined Portugal's near monopoly on the lucrative oceanic spice and slave trades. This sent the Portuguese spice trade into a long decline.  The diversion of wealth from Portugal by the Habsburg monarchy to support the Catholic side of the Thirty Years' War also created strains within the union, although Portugal did also benefit from Spanish military power in helping to retain Brazil and in disrupting Dutch trade. These events, and those that occurred at the end of Aviz dynasty and the Iberian Union, led Portugal to a state of dependency on its colonies, first India and then Brazil.
The joining of the two crowns deprived Portugal of a separate foreign policy, and Spain's enemies became Portugal's. England had been an ally of Portugal since the Treaty of Windsor in 1386. War between Spain and England led to a deterioration of the relations with Portugal's oldest ally, and the loss of Hormuz. English help provided by Elizabeth I of England in a rebellion against the kings assured the survival of the alliance. War with the Dutch led to invasions of many countries in Asia, including Ceylon (today's Sri Lanka), and commercial interests in Japan, Africa (Mina), and South America. Even though Portuguese were unable to capture the entire island of Ceylon, they were able to keep the coastal regions of Ceylon under their control for a considerable time. Brazil was partially conquered by both France and the Seventeen Provinces.
In the 17th Century, taking advantage of this period of Portuguese weakness, many Portuguese territories in Brazil were occupied by the Dutch who gained access to the sugarcane plantations. John Maurice, Prince of Nassau-Siegen was appointed as the governor of the Dutch possessions in Brazil in 1637 by the Dutch West India Company. He landed at Recife, the port of Pernambuco, in January 1637. By a series of successful expeditions, he gradually extended the Dutch possessions from Sergipe on the south to São Luís de Maranhão in the north. He likewise conquered the Portuguese possessions of Elmina Castle, Saint Thomas, and Luanda, Angola, on the west coast of Africa. After the dissolution of the Union in 1640, Portugal reestablished its authority over the lost territories of the Portuguese Empire. The Dutch intrusion into Brazil was long lasting and troublesome to Portugal. The Seventeen Provinces captured a large portion of the Brazilian coast including Bahia (and its capital Salvador) and Pernambuco (and its capital Olinda). The whole Brazilian northeast was occupied but the Dutch conquest was short lived. The recapture of Salvador by a Spanish-Portuguese fleet in 1625 was followed by a rapid recovery of the lost territories. The Dutch returned in 1630 and captured Recife and Olinda in the captaincy of Pernambuco, the largest and richest sugar-producing area in the world. This began a war over Brazil, which would see the Dutch establish a colony called New Holland. However, the Second Battle of Guararapes, second and decisive battle in a conflict called Pernambucana Insurrection, ended the Dutch occupation of the Portuguese colony of Brazil.
On the other hand, the Iberian Union opened to both countries a worldwide span of control, as Portugal dominated the African and Asian coasts that surrounded the Indian Ocean, and Spain the Pacific Ocean and both sides of Central and South America, while both shared the Atlantic Ocean space.
Iberian Union