This map shows that most of the Spanish Empire, particularly in the Americas, suddenly, within 50 years collapse into a great number of nation states.
The question is how and why the sudden collapse?
TL;DR It seemed that the whole invasion by France in the Napoleonic Wars was a major influence on the biggest collapse of the Spanish Empire (I'm not counting the end of the century final collapse of what was left), even though Spain had been really weakened for more than a century before that.
I wouldn't call the the collapse of the Spanish Empire sudden. Based on my encounters with Spanish history from the Stuart period to the end of the Napoleonic Era, they slowly got weaker over time and then the Napoleonic Wars was the foot that came through the thinned and rotted floor.
I always got the impression that Spain and its empire was in decline starting about the time when other countries start to heavily establish firm colonies in the western hemisphere. That was already done by about the 1660s. In the second half of the 17th century, Spain had pretty certainly lost its hold on the Netherlands and Portugal (both of those circumstances were established in the previous half the century). The New World colonies were also the frequent target of attacks by raiders, the buccaneers. New World Spanish naval power went down significantly in the 17th century. Based on what I gathered from the book Trafalgar and the Spanish Navy by John D. Harbron (which has a notable section that covers Spanish naval power from about 1700 on), Spain had no real national fleet by 1700 (just some really weak small local fleets of warships and a couple of commercial fleets), and by 1700 had not built new warships for almost 2 decades. They lost Gibraltar in the War of Spanish Succession, and had the Bourbons come into rule in the country. While the Bourbons helped the country rebound a little bit over the course of the 18th century in terms of military and navy power, Spain would never be one of the top two naval powers (or European powers in general for that matter) again.
At the mid 18th-century mark, Spain was still suffering defeats in their colonies - Havana was captured (but they negotiated the return of that) and Florida was also captured and remained under British rule for some time (they get it back in 1783 because of the Treaty of Paris - Spain came in on the American side later in the War). The early-eighteenth century also marked serious problems along the northern border of New Spain with conflicts involving American Indians. Overall, the colonies of the New World were doing quite poorly from the later 17th century to 1800. Spain did what they could, but the demand for products from Spain severely outstripped what was supplied. Spain bought into mercantilism too, but were quite bad at enforcing it. the Guardas de las Costas of the era regularly went out to stop non-Spanish ships from going to Spanish colonies and engaging in illegal trade (though the Guardas de las Costas more often than not just took ships for the profit of taking them).
While Spain built up a navy and military that could at least "get up and toe the line" to use an old boxing analogy (but if that Spanish Navy and Army were big and good enough to win is another matter), then the Napoleonic wars severely messed up things. Spain was invaded and taken by France. There were struggles to control Spain, with the populace splitting over supporting the French puppet government or rebellion. Also, Napoleon pulled off the Third Treaty of San Ildefonso in secret in 1800, giving the Louisiana Territory back to France (France lost it to Spain in the aftermath of the Seven Years War) - and then Napoleon quickly sold that for cash to the United States (the people in the Louisiana Territory didn't know until just before the sale that France owned the territory again). So, with Spain occupied in a struggle with France's occupation, and with how poor Spain's possessions were, of course they are going to try and break off from Spain. Spain was also in a pretty tight spot in terms of finances after the war, they have to recover - so that also doesn't help with maintaining or recovering an empire. Granted, they still kept some parts of their empire through most of the 19th century (and then Spanish-American War happened in 1898).
So the moral of the story is - it's well enough to establish an empire - but upkeep is another issue, and then having to deal with neighbors dragging you into constant warfare (which is easy enough for bankrupting your treasuries), having those same neighbors try and take away parts of said empire (or make colonies in parts you somewhat neglected), trying to control the economies of your empire (but to do it poorly), and to then get occupied by another nation...can you see the problems mounting?
In addition to the strong descriptions of Spain’s military and financial troubles made by /u/davidAOP and /u/richard0copeland, I think it is very important to discuss the colonists in the New World who were just as important to the dissolution of the Spanish Empire as the military and financial problems. Although the financial and military problems were significant, I would argue that the collapse of the Spanish Empire was very much a sudden event caused almost exclusively by the power vacuum brought about by Napoleon’s invasion of Spain.
Surprisingly, there was very little that actually held the Spanish Empire together throughout the colonial period. The Spanish Empire was such a vast space that population centers were separated from each other by vast gulfs of sparsely populated wilderness and seemingly impenetrable geographic barriers. As a result, individual colonies (and even localities within each colony) developed their own identities that emphasized their respective interests. Thus, there was virtually no unity between colonies, only loyalty to the Spanish Crown. So when Napoleon invaded Spain in 1808, he untied the only institution that truly held the empire together.
In the ensuing power vacuum, various individuals and groups on both sides of the Atlantic sought to pursue their own interests. For example, Creole elites in the Americas demanded that they receive equality and free trade opportunities which had previously been denied to them, but when these petitions were rejected by juntas in Spain, these American leaders declared independence--not from Spain (initially) but from the reign of Spanish citizen juntas. When King Ferdinand did return and attempted to rein in the colonies’ independence, they broke outright from Spain. Yet, Spain was still powerful enough to nearly crush these rebellions. By the late 1810s, only the Río de la Plata region remained rogue. Spain had even amassed a massive invasion force, which was supposedly going to put an end to the rebellion there too, but before the invasion force left, officers in the army rebelled against the king. This gave the American leaders the time they needed to swing the tide against Spanish loyalists in America. By the mid 1820s virtually all of the Spanish colonies had slipped from Spain’s grasp.
Yet to talk about only the military, finance, and elite creoles is to ignore how the average people of America also participated in the breakdown of Spanish power. People from all walks of life found opportunities and challenges in the chaos. Some joined up with leaders to defend their homeland against outsiders (whether they were Spanish loyalists sent to retake power or military forces from other colonies [and even nearby cities] seeking to exert their own control over a locality). Others found company in “alternative movements” that recognized neither Spanish nor creole authority in population centers. Still others simply tried to keep their heads down and maintain the lifestyles and cultures that they had seemingly always led. Indigenous groups often enjoyed increased autonomy; slaves found independence in liberal armies; and merchants took the opportunity to pursue economic opportunities that were previously closed to them.
Thus, though there were problems in the Spanish Empire prior to 1808, the forces unleashed by Napoleon’s invasion took on a life of their own, which Spain was unable to control. The lack of unity ushered in a fifty year period of power renegotiation, often violent and chaotic, that eventually led to the foundation of the nation-states we see today.
Sources:
From "To rule the Waves" Arthur Herman
"Yet this multicontinent empire, for all it's vast territories, diverse resources, and awesome power, increasingly depended on a single slender thread to survive. This was the thread of silver.
.......so the future of his (Philip II) entire empire hinged on the annual arrival of the American silver fleet.
And yet, incredibly, Spain had no full time fleet to protect this vital lifeline.
......But Hawkins and Drake realized that the flotas were the true lifeline of Philip's empire. If they could cut that silver cord, they could bring that mighty silver empire to it's knees, and with it, the Antichrist."
I, too, wouldn't exactly call the collapse of the Spanish Empire 'sudden' either -it was a long slow decline- but Hawkins, Drake, et al certainly had a huge hand in starting the ball rolling
