Final answer:
Piracy aided empire-building by disrupting rivals but also threatened empires by requiring them to increase naval defense spending. The decline of piracy was largely due to the Royal Navy's dominance following the Napoleonic Wars, particularly during the Pax Britannica.
Step-by-step explanation:
During the European colonial period, piracy became an instrument of empire-building as it disrupted the trade routes and shipping of rival empires. Pirates would attack merchant ships to seize goods and undermine the economic stability of competing nations. However, piracy also threatened empires by challenging their control of the seas, leading to increased military and naval expenditures in order to protect trade and transport.
What culminated in the decline of piracy was the establishment of stronger naval forces, particularly the Royal Navy under British hegemony. After the defeat of Napoleon at the Battle of Waterloo in 1815, the British Navy gained control over the world's shipping lanes, which enabled them to effectively block most piracy. This era, known as the Pax Britannica, saw Britain become the world's arbitrator, significantly reducing the acts of piracy through their naval dominance.